IN  MEMORY 

of 

'Ol'fcinent  A.   Whiting 


'Y   ^6 


PRESENTED  BY 

Dr.  Lillian  Berlier 


J 

*  A.. 


UNIVERSITY  OF  CALIFORNIA 

CALIFORNIA  .COLLEGE  OF  MEDICINE 

LIBRARY 

AUG     8  1972 
IRVINE,  CALIFORNIA  92664 


V 


LOUIS   PASTEUE 


UEFf-FY  OF 
fni  LEC-E  OF  GGTEGFATKl 

LOUIS  PASTEUR. j 


HIS    LIFE    AJSTD    LABOUES 


BY  HIS  SON-IN-LAW 


TRANSLATED  FEOM  THE  FBENCH 
BY 

LADY    CLAUD    HAMILTON 


V/ 


/  JYJW 


NEW   YORK 

D.   APPLETON    AND    COMPANY 
1,  3,  AND    5   BOND    STREET 

1885. 


W2  100 

1/3 


PREFACE. 


IN  the  salon  of  a  distinguished  man,  or  of  a  great 
writer,  there  is  often  to  be  found  a  person  who,  without 
being  either  a  fellow-worker  or  a  disciple,  without 
even  possessing  the  scientific  or  literary  qualities  which 
might  explain  his  habitual  presence,  lives  nevertheless 
in  complete  familiarity  with  the  man  whom  all  around 
him  call  '  dear  master.'  Whence  comes  this  intimate 
one  ?  who  is  he  ?  what  is  his  business  ?  He  is  only 
known  as  a  friend  of  the  house.  He  has  no  other 
title,  and  he  is  almost  proud  of  having  no  other. 
Stripped  of  his  own  personality,  he  speaks  only  of  the 
labours  and  the  success  of  his  illustrious  friend,  in 
the  radiance  of  whose  glory  he  moves  with  delight. 

The  author  of  this  work  is  a  person  of  this  descrip- 
tion. Intimately  connected  with  the  life  of  M.  Pasteur, 
and  a  constant  inmate  of  his  laboratory,  he  has  passed 
happy  years  near  this  great  investigator,  who  has  dis- 
covered a  new  world — the  world  of  the  infinitely  little. 
Since  the  first  studies  of  M.  Pasteur  on  molecular 


VI  PREFACE. 

dissymmetry,  down  to  his  most  recent  investigations 
on  hydrophobia,  on  virulent  diseases,  and  on  the  arti- 
ficial cultures  of  living  contagia,  which  have  been 
converted  by  such  cultures  into  veritable  vaccines — 
passing  by  the  intermediate  celebrated  experiments  on 
spontaneous  generation,  fermentation,  the  diseases  of 
wine,  the  manufacture  of  beer  and  vinegar,  and  the 
diseases  of  silkworms — the  author  of  these  pages  has 
been  able,  if  not  to  witness  all,  at  least  to  follow  in 
its  principal  developments  this  uninterrupted  series  of 
scientific  conquests. 

'  What  a  beautiful  book,'  he  remarked  one  day  to 
M.  Pasteur,  '  might  be  written  about  all  this  ! ' 

'But  it  is  all  in  the  Comptes-rendus  of  the 
Academy  of  Sciences/ 

'  It  is  not  for  the  readers  of  the  Comptes-rendus 
that  such  a  book  needs  to  be  written,  but  for  the  great 
public,  who  know  that  you  have  done  great  things, 
but  who  know  it  only  vaguely,  by  the  records  of 
journals,  or  by  fragments  of  biography.  The  persons 
are  few  who  know  the  history  of  your  discoveries. 
What  was  your  point  of  departure  ?  How  have  you 
arrived  at  such  and  such  principles,  and  at  the  conse- 
quences which  flow  from  these  principles  ?  What  is 
the  connection  and  rigorous  bond  of  your  method  ? 
These  are  the  things  which  it  would  be  interesting  to 
put  together  in  a  book  which  would  have  some  chance 
of  enduring  as  an  historic  document.' 


PREFACE.  yii 

'  I  could  not  waste  my  time  in  going  back  upon 
things  already  accomplished.' 

'  No ;  but  my  desire  is  that  someone  else  should 
consecrate  his  time  to  the  work.  And  listen/  added 
this  friend,  with  audacious  frankness — '  do  you  know 
by  whom,  in  my  opinion,  this  book  ought  to  be 
written  ?  By  a  man  who,  without  having  been  in 
any  way  trained  to  follow  in  your  footsteps,  is  ani- 
mated by  the  most  lively  desire  to  understand  the 
course  which  you  have  pursued  ;  who,  while  living  at 
your  side,  has  been  each  day  impregnated  with  your 
method  and  your  ideas  ;  who,  having  had  the  happi- 
ness of  comprehending  your  life  and  its  achievements, 
does  not  wish  to  confine  the  pleasure  thus  derived  to 
himself  alone.' 

'  Where,  then,'  interrupted  Pasteur  with  a  kindly 
smile,  not  without  a  tinge  of  irony,  '  is  this  man,  at 
once  so  happy,  and  so  impatient  to  share  his  happi- 
ness with  others  ? ' 

'  He  is  now  pleading  his  cause  before  you.  Yes, 
I  would  gladly  attempt  such  a  work.  I  have  seen 
your  efforts  and  observed  your  success.  The  experi- 
ments which  I  have  not  witnessed  you  have  always 
freely  explained  to  me,  with  that  gift  of  clearness 
which  Vauvenargues  called  the  "polish"  of  masters.1 
Initiated  by  affection,  I  would  make  myself  initiator 
by  admiration.  It  would  be  the  history  of  a  learned 

1  '  Vernis  des  maitres.' 


Vlll  PBEFACE. 

man  by  an  ignorant  one.  My  ignorance  would  save 
me  from  dwelling  too  strictly  or  too  long  on  technical 
details.  With  the  exposition  of  your  doctrine  I  would 
mingle  some  fragments  of  your  biography.  I  would 
pass  from  a  discovery  to  an  anecdote,  and  so  arrange 
matters  as  to  give  the  book  not  only  the  character 
of  a  familiar  scientific  conversation,  which  would 
hardly  be  more  than  the  echo  of  what  I  have  learnt 
while  near  you,  but  also  to  make  it  a  reflex  of  your 
life.' 

'  You  should  postpone  that  until  I  am  no  longer 


'  Why  so  ?  Why,  before  assigning  to  them  their 
places,  should  we  wait  till  those  whose  names  will  en- 
dure have  disappeared  from  the  scene  ?  No  ;  it  is  you, 
living,  that  I  wish  to  paint  —  you,  in  full  work,  in  the 
midst  of  your  laboratory.  And,  in  addition  to  all 
other  considerations,  I  would  add,  that  your  presence 
in  the  flesh  will  be  the  guarantee  of  my  exactitude.' 

July  188a 


CONTENTS. 


PACK 

INTRODUCTION,   BY   PBOFESSOR   TYNDALL      .     .           .           .           .  xi 

RECOLLECTIONS  OF  CHILDHOOD  AND  YOUTH — FIRST  DISCOVERIES  1 

FERHENTATION 40 

ACETIC   FERMENTAT  ON — THE   MANUFACTURE   OF    VINEGAR         .  66 

THE   QUESTION   OF   SPONTANEOUS   GENERATION    .           .           .      .  89 

EIUDIES   ON   WINE 112 

THE  SILKWORM-DISEASE 127 

DECISIVE   EXPERIMENTS 164 

STUDIES   ON   BEER 168 

VIRULENT   DISEASES — SPLENIC   FEVER,   SEPTICAEMIA           .           .  176 

FOWL   CHOLERA 212 

ATTENUATED    VIRUS,   OR    VACCINATION — THE    FOWL    CHOLERA 

VACCINE 220 

THE  VACCINE   OP   SPLENIC   FEVER         .           .           .                       .      .  231 

THE   RETURN   TO   VIRULENCE 246 

ETIOLOGY   OF   SPLENIC   FEVER 250 

METHOD   OF   DISCUSSION   AND   CONTRADICTIONS  .  .  .262 

THE   LABORATORY    OF   THE  ECOLE  NORMALE-  VARIOUS   STUDIES 

— HYDROPHOBIA 271 


INTBODUCTION. 


IN  the  early  part  of  the  present  year  the  French 
original  of  this  work  was  sent  to  me  from  Paris  by 
its  author.  It  was  accompanied  by  a  letter  from 
M.  Pasteur,  expressing  his  desire  to  have  the  work 
translated  and  published  in  England.  Eesponding  to 
this  desire,  I  placed  the  book  in  the  hands  of  the 
Messrs.  Longman,  who,  in  the  exercise  of  their  own 
judgment,  decided  on  publication.  The  translation  was 
confided,  at  my  suggestion,  to  Lady  Claud  Hamilton. 

The  translator's  task  was  not  always  an  easy  one, 
but  it  has,  I  think,  been  well  executed.  A  few  slight 
abbreviations,  for  which  I  am  responsible,  have  been 
introduced,  but  in  no  case  do  they  affect  the  sense. 
It  was,  moreover,  found  difficult  to  render  into  suitable 
English  the  title  of  the  original :  '  M.  Pasteur,  His- 
toire  d'un  Savant  par  un  Ignorant.'  A.  less  piquant  and 
antithetical  English  title  was,  therefore,  substituted  for 
the  French  one. 

This  filial  tribute,  for  such  it  is,  was  written,  under 
the  immediate  supervision  of  M.  Pasteur,  by  his 


X1J  INTKODUCTION. 

devoted  and  admiring  son-in-law,  M.  Valery  Radot.  It 
is  the  record  of  a  life  of  extraordinary  scientific  ardour 
and  success,  the  picture  of  a  mind  on  which  facts  fall 
like  germs  upon  a  nutritive  soil,  and,  like  germs  so 
favoured,  undergo  rapid  increase  and  multiplication. 
One  hardly  knows  which  to  admire  most — the  in- 
tuitive vision  which  discerns  in  advance  the  new 
issues  to  which  existing  data  point,  or  the  skill  in 
device,  the  adaptation  of  means  to  ends,  whereby  the 
intuition  is  brought  to  the  test  and  ordeal  of  experi- 
ment. 

In  the  investigation  of  microscopic  organisms — the 
'  infinitely  little,'  as  Pouchet  loved  to  call  them — and 
their  doings  in  this  our  world,  M.  Pasteur  has  found 
his  true  vocation.  In  this  broad  field  it  has  been  his 
good  fortune  to  alight  upon  a  crowd  of  connected 
problems  of  the  highest  public  and  scientific  interest, 
ripe  for  solution,  and  requiring  for  their  successful 
treatment  the  precise  culture  and  capacities  which  he 
has  brought  to  bear  upon  them.  He  may  regret  his 
abandonment  of  molecular  physics;  he  may  look 
fondly  back  upon  the  hopes  with  which  his  researches 
on  the  tartrates  and  paratartrates  inspired  him;  he 
may  think  that  great  things  awaited  him  had  he 
continued  to  labour  in  this  line.  I  do  not  doubt  it. 
But  this  does  not  shake  my  conviction  that  he  yielded 
to  the  natural  affinities  of  his  intellect,  that  he  obeyed 
its  truest  impulses,  and  reaped  its  richest  rewards,  in 


INTRODUCTION.  X1U 

pursuing  the  line  that  he  has  chosen,  and  in  which 
his  labours  have  rendered  him  one  of  the  most  con- 
spicuous scientific  figures  of  this  age. 

With  regard  to  the  earliest  labours  of  M.  Pasteur, 
a  few  remarks  supplementary  to  those  of  M.  Eadot 
may  be  introduced  here.  The  days  when  angels 
whispered  into  the  hearkening  human  ear,  secrets 
which  had  no  root  in  man's  previous  knowledge  or 
experience,  are  gone  for  ever.  The  only  revelation — 
and  surely  it  deserves  the  name — now  open  to  the  wise 
arises  from  '  intending  the  mind  '  on  acquired  know- 
ledge. When,  therefore,  M.  Eadot,  following  M.  Pas- 
teur, speaks  with  such  emphasis  about  '  preconceived 
ideas,'  he  does  not  mean  ideas  without  antecedents. 
Preconceived  ideas,  if  out  of  deference  to  M.  Pasteur 
the  term  be  admitted,  are  the  vintage  of  garnered 
facts.  We  in  England  should  rather  call  them  induc- 
tions, which,  as  M.  Pasteur  truly  says,  inspire  the 
mind,  and  shape  its  course,  in  the  subsequent  work 
of  deduction  and  verification. 

At  the  time  when  M.  Pasteur  undertook  his  inves- 
tigation of  the  diseases  of  silkworms,  which  led  to 
such  admirable  results,  he  had  never  seen  a  silkworm ; 
but,  so  far  from  this  being  considered  a  disqualification, 
M.  Dumas  regarded  his  freedom  from  preconceived 
ideas  a  positive  advantage.  His  first  care  was  to 
make  himself  acquainted  with  what  others  had  done. 
To  their  observations  he  added  his  own,  and  then, 


xiv  INTEODTJCTION. 

surveying  all,  came  to  the  conclusion  that  the  origin 
of  the  disease  was  to  be  sought,  not  in  the  worms,  not 
in  the  eggs,  but  in  the  moths  which  laid  the  eggs.  I 
am  not  sure  that  this  conclusion  is  happily  described 
as  .'  a  preconceived  idea.'  Every  whipster  may  have 
his  preconceived  ideas ;  but  the  divine  power,  so 
largely  shared  by  M.  Pasteur,  of  distilling  from  facts 
their  essences — of  extracting  from  them  the  principles 
from  which  they  flow — is  given  only  to  a  few. 

With  regard  to  the  discovery  of  crystalline  facets 
in  the  tartrates,  which  has  been  dwelt  upon  by 
M.  Kadot,  a  brief  reference  to  antecedent  labours  may 
be  here  allowed.  It  had  been  discovered  by  Arago, 
in  1811,  and  by  Biot,  in  1812  and  1818,  that  a  plate 
of  rock-crystal,  cut  perpendicular  to  the  axis  of  the 
prism,  possessed  the  power  of  rotating  the  plane  of 
polarisation  through  an  angle,  dependent  on  the  thick- 
ness of  the  plate  and  the  refrangibility  of  the  light. 
It  had,  moreover,  been  proved  by  Biot  that  there  existed 
two  species  of  rock-crystal,  one  of  which  turned  the 
plane  of  polarisation  to  the  right,  and  the  other  to  the 
left.  They  were  called,  respectively,  right-handed  and 
left-handed  crystals.  No  external  difference  of  crystal- 
line form  was  at  first  noticed  which  could  furnish  a 
clue  to  this  difference  of  action.  But  closer  scrutiny 
revealed  upon  the  crystals  minute  facets,  which,  in 
the  one  class,  were  ranged  along  a  right-handed,  and, 


INTRODUCTION.  XV 

in  the  other,  along  a  left-handed  spiral.  The  symmetry 
of  the  hexagonal  prism,  and  of  the  two  terminal 
pyramids  of  the  crystal,  was  disturbed  by  the  intro- 
duction of  these  spirally-arranged  facets.  They  con- 
stituted the  outward  and  visible  sign  of  that  inward 
and  invisible  molecular  structure  which  produced  the 
observed  action,  and  difference  of  action,  on  polarised 
light. 

When,  therefore,  the  celebrated  Mitscherlich 
brought  forward  his  tartrates  and  paratartrates  of 
ammonia  and  soda,  and  affirmed  them  to  possess  the 
same  atoms,  the  same  internal  arrangement  of  atoms, 
and  the  same  outward  crystalline  form,  one  of  them, 
nevertheless,  causing  the  plane  of  polarisation  to 
rotate,  while  the  other  did  not,  Pasteur,  remember- 
ing, no  doubt,  the  observations  just  described,  insti- 
tuted a  search  for  facets  like  those  discovered  in 
rock-crystal,  and  which,  without  altering  chemical 
constitution,  destroyed  crystalline  identity.  He  first 
found  such  facets  in  the  tartrates,  while  he  subse- 
quently proved  the  neutrality  of  the  paratartrate  to 
be  due  to  the  equal  admixture  of  right-handed  and 
left-handed  crystals,  one  of  which,  when  the  para- 
tartrate was  dissolved,  exactly  neutralised  the  other. 

Prior  to  Pasteur  the  left-handed  tartrate  was 
unknown.  Its  discovery,  moreover,  was  supplemented 
by  a  series  of  beautiful  researches  on  the  compounds  of 
right-handed  and  left-handed  tartaric  acid ;  he  having 


xvi  INTRODUCTION. 

previously  extracted  from  the  two  tartrates,  acids  which, 
in  regard  to  polarised  light,  behaved  like  themselves. 
Such  was  the  worthy  opening  of  M.  Pasteur's  scientific 
career,  which  has  been  dwelt  upon  so  frequently  and 
emphatically  by  M.  Kadot.  The  wonder,  however, 
is,  not  that  a  searcher  of  such  penetration  as  Pasteur 
should  have  discovered  the  facets  of  the  tartrates, 
but  that  an  investigator  so  powerful  and  experienced 
as  Mitscherlich  should  have  missed  them. 

The  idea  of  molecular  dissymmetry,  introduced 
by  Biot,  was  forced  upon  Biot's  mind  by  the  discovery 
of  a  number  of  liquids,  and  of  some  vapours,  which 
possessed  the  rotatory  power.  Some,  moreover,  turned 
the  plane  of  polarisation  to  the  right,  others  to  the 
left.  Crystalline  structure  being  here  out  of  the 
question,  the  notion  of  dissymmetry,  derived  from 
the  crystal,  was  transferred  to  the  molecule.  '  To 
produce  any  such  phenomena,'  says  Sir  John  Herschel, 
'  the  individual  molecule  must  be  conceived  as  un- 
symrnetrically  constituted.'  The  illustrations  employed 
by  M.  Pasteur  to  elucidate  this  subject,  though  well 
calculated  to  give  a  general  idea  of  dissymmetry,  will, 
I  fear,  render  but  little  aid  to  the  reader  in  his  at- 
tempts to  realise  molecular  dissymmetry.  Should 
difficulty  be  encountered  here  at  the  threshold  of  this 
work,  I  would  recommend  the  reader  not  to  be  daunted 
by  it,  or  prevented  by  it  from  going  further.  He  may 
comfort  himself  by  the  assurance  that  the  conception 


INTKODUCTION.  XV11 

of  a  dissymmetric  molecule  is  not  a  very  precise  one, 
even  in  the  mind  of  M.  Pasteur. 

One  word  more  with  regard  to  the  parentage  of 
preconceived  ideas.  M.  Eadot  informs  us  that  at 
Strasburg  M.  Pasteur  invoked  the  aid  of  helices  and 
magnets,  with  a  view  to  rendering  crystals  dissym- 
metrical at  the  moment  of  their  formation.  There 
can,  I  think,  be  but  little  doubt  that  such  experiments 
were  suggested  by  the  pregnant  discovery  of  Faraday 
published  in  1845.  By  both  helices  and  magnets 
Faraday  caused  the  plane  of  polarisation  in  perfectly 
neutral  liquids  and  solids  to  rotate.  If  the  turning  of 
the  plane  of  polarisation  be  a  demonstration  of  mole- 
cular dissymmetry,  then,  in,  the  twinkling  of  an  eye, 
Faraday  was  able  to  displace  symmetry  by  dissym- 
metry, and  to  confer  upon  bodies,  which  in  their 
ordinary  state  were  inert  and  dead,  this  power  of 
rotation  which  M.  Pasteur  considers  to  be  the  ex- 
clusive attribute  of  life. 

The  conclusion  of  M.  Pasteur  here  referred  to 
which  M.  Eadot  justly  describes  as  '  worthy  of  the 
most  serious  consideration,'  is  sure  to  arrest  the 
attention  of  a  large  c'ass  of  people,  who,  dreading 
'  materialism,'  are  ready  to  welcome  any  generalisa- 
tion which  differentiates  the  living  world  from  the 
dead.  M.  Pasteur  considers  that  his  researches  point 
to  an  irrefragable  physical  barrier  between  organic 
and  inorganic  nature.  Never,  he  says,  have  you  been 


XV111  INTRODUCTION. 

able  to  produce  in  the  laboratory,  by  the  ordinary 
processes  of  chemistry,  a  dissymmetric  molecule — in 
other  words,  a  substance  which,  in  a  state  of  solution, 
where  molecular  forces  are  paramount,  has  the  power 
of  causing  a  polarised  beam  to  rotate.  This  power 
belongs  exclusively  to  derivatives  from  the  living  world. 
Dissymmetric/on-es,  different  from  those  of  the  labora- 
tory, are,  in  Pasteur's  mind,  the  agents  of  vitality ;  it  is 
they  that  build  up  dissymmetric  molecules  which  baffle 
the  chemist  when  he  attempts  to  reproduce  them.  Such 
molecules  trace  their  ancestry  to  life  alone.  '  Pour- 
rait-on  indiquer  une  separation  plus  profonde  entre  les 
produits  de  la  nature  vivante,  et  ceux  de  la  nature 
minerale,  que  cette  dissymmetric  chez  les  uns,  et  son 
absence  chez  les  autres  ? '  It  may  be  worth  calling 
to  mind  that  molecular  dissymmetry  is  the  idea,  or 
inference,  the  observed  rotation  of  the  plane  of  polari- 
sation, by  masses  of  sensible  magnitude,  being  the  fact 
on  which  the  inference  is  based. 

That  the  molecule,  or  unit  brick,  of  an  organism 
should  be  different  from  the  molecule  of  a  mineral  is 
only  to  be  expected,  for  otherwise  the  profound  dis- 
tinction between  them  would  disappear.  And  that 
one  of  the  differences  between  the  two  classes  of 
molecules  should  be  the  possession,  by  the  one,  of 
this  power  of  rotation,  and  its  non-possession  by  the 
other,  would  be  a  fact,  interesting  no  doubt,  but  not 
surprising.  The  critical  point  here  has  reference  to 


INTRODUCTION.  XIX 

the  power  and  range  of  chemical  processes,  apart  from 
the  play  of  vitality.  Beginning  with  the  elements 
themselves,  can  they  not  be  so  combined  as  to  produce 
organic  compounds  ?  Not  to  speak  of  the  antecedent 
labours  of  Wohler  and  others  in  Germany,  it  is  well 
known  that  various  French  investigators,  among  whom 
are  some  of  M.  Pasteur's  illustrious  colleagues  of  the 
Academy,  have  succeeded  in  forming  substances  which 
were  once  universally  regarded  as  capable  of  being 
elaborated  by  plants  and  animals  alone.  Even  with 
regard  to  the  rotation  of  the  plane  of  polarisation,  M. 
Jungfleisch,  an  extremely  able  pupil  of  the  celebrated 
Berthelot,  affirms  that  the  barrier  erected  by  M.  Pas- 
teur has  been  broken  down ;  and  though  M.  Pasteur 
questions  this  affirmation,  it  is  at  least  hazardous, 
where  so  many  supposed  distinctions  between  organic 
and  inorganic  have  been  swept  away,  to  erect  a  new 
one.  For  my  part,  I  frankly  confess  my  disbelief  in 
its  permanence. 

Without  waiting  for  new  facts,  those  already  in 
our  possession  tend,  I  think,  to  render  the  association 
which  M.  Pasteur  seeks  to  establish  between  dissym- 
metry and  life  insecure.  Quartz,  as  a  crystal,  exerts 
a  very  powerful  twist  on  the  plane  of  polarisation. 
Quartz  dissolved  exerts  no  power  at  all.  The  mole- 
cules of  quartz,  then,  do  not  belong  to  the  same  category 
as  the  crystal  of  which  they  are  the  constituents;  the 
former  are  symmetrical,  the  latter  is  dissymmetrical. 


XX  INTRODUCTION. 

This,  in  my  opinion,  is  a  very  significant  fact.  By  the 
act  of  crystallisation,  and  without  the  intervention  of 
life,  the  forces  of  molecules,  possessing  planes  of  sym- 
metry, are  so  compounded  as  to  build  up  crystals  which 
have  no  planes  of  symmetry.  Thus,  in  passing  from 
the  symmetrical  to  the  dissymmetrical,  we  are  not  com- 
pelled to  interpolate  new  forces ;  the  forces  extant  in 
mineral  nature  suffice.  The  reasoning  which  applies 
to  the  dissymmetric  crystal  applies  to  the  dissymmetric 
molecule.  The  dissymmetry  of  the  latter,  however 
pronounced  and  complicated,  arises  from  the  compo- 
sition of  atomic  forces  which,  when  reduced  to  their 
most  elementary  action,  are  exerted  along  straight 
lines.  In  1865  I  ventured,  in  reference  to  this  subject, 
to  define  the  position  which  I  am  still  inclined  to  main- 
tain. '  It  is  the  compounding,  in  the  organic  world, 
of  forces  belonging  equally  to  the  inorganic  that  con- 
stitutes the  mystery  and  the  miracle  of  vitality.' l 

Add  to  these  considerations  the  discovery  of 
Faraday  already  adverted  to.  An  electric  current  is 
not  an  organism,  nor  does  a  magnet  possess  life ;  still, 
by  their  action,  Faraday,  in  his  first  essay,  converted 
over  one  hundred  and  fifty  symmetric  and  inert 
aqueous  solutions  into  dissymmetric  and  active  ones.2 

1  Art.  '  Vitality,'  Fragments  of  Science,  6th  edit.,  vol.  ii.  p.  50. 

1  In  Faraday's  induced  dissymmetry  the  ray,  having  once  passed 
through  the  body  under  magnetic  influence,  has  its  rotation  doubled, 
instead  of  neutralised,  as  in  the  case  of  quartz,  on  being  reflected 
back  through  the  body.  Marbach  has  discovered  that  chlorate  of 


INTRODUCTION.  XXI 

Theory,  however,  may  change,  and  inference  may 
fade  away,  but  scientific  experiment  endures  for  ever. 
Such  durability  belongs,  in  the  domain  of  molecular 
physics,  to  the  experimental  researches  of  M.  Pasteur. 

The  weightiest  events  of  life  sometimes  turn  upon 
small  hinges  ;  and  we  now  come  to  the  incident  which 
caused  M.  Pasteur  to  quit  a  line  of  research  the 
abandonment  of  which  he  still  regrets.  A  German 
manufacturer  of  chemicals  had  noticed  that  the  im- 
pure commercial  tartrate  of  lime,  sullied  with  organic 
matters  of  various  kinds,  fermented  on  being  dissolved 
in  water  and  exposed  to  summer  heat.  Thus  prompted, 
Pasteur  prepared  some  pure,  right-handed  tartrate  of 
ammonia,  mixed  with  it  albuminous  matter,  and  found 
that  the  mixture  fermented.  His  solution,  limpid  at 
first,  became  turbid,  and  the  turbidity  he  found  to  be 
due  to  the  multiplication  of  a  microscopic  organism, 
which  found  in  the  liquid  its  proper  aliment.  Pasteur 
recognised  in  this  little  organism  a  living  ferment. 
This  bold  conclusion  was  doubtless  strengthened,  if 
not  prompted,  by  the  previous  discovery  of  the  yeast- 
plant — the  alcoholic  ferment — by  Cagniard-Latour 
and  Schwann. 

Pasteur  next  permitted  his  little  organism  to  take 

soda  produces  circular  polarisation  in  all  directions  through  the 
crystal,  while  in  quartz  it  occurs  only  in  the  direction  of  the  axis. 
Marbach  also  discovered  facets  upon  his  crystals,  resembling  those 
of  quartz. 


xxii  INTRODUCTION. 

the  carbon  necessary  for  its  growth  from  the  pure 
paratartrate  of  ammonia.  Owing  to  the  opposition 
of  its  two  classes  of  crystals,  a  solution  of  this  salt, 
it  will  be  remembered,  does  not  turn  the  plane  of  polar- 
ised light  either  to  the  right  or  to  the  left.  Soon 
after  fermentation  had  set  in,  a  rotation  to  the  left 
was  noticed,  proving  that  the  equilibrium  previously 
existing  between  the  two  classes  of  crystals  had  ceased. 
The  rotation  reached  a  maximum,  after  which  it  was 
found  that  all  the  right-handed  tartrate  had  disap- 
peared from  the  liquid.  The  organism  thus  proved 
itself  competent  to  select  its  own  food.  It  found,  as 
it  were,  one  of  the  tartrates  more  digestible  than  the 
other,  and  appropriated  it,  to  the  neglect  of  the  other. 
No  difference  of  chemical  constitution  determined  its 
choice ;  for  the  elements,  and  the  proportions  of  the 
elements,  in  the  two  tartrates  were  identical.  But  the 
peculiarity  of  structure  which  enabled  the  substance  to 
rotate  the  plane  of  polarisation  to  the  right,  also  ren- 
dered it  a  fit  aliment  for  the  organism.  This  most 
remarkable  experiment  was  successfully  made  with  the 
seeds  of  our  common  mould,  Penicillium  glaucwn. 

Here  we  find  Pasteur  unexpectedly  landed  amid 
the  phenomena  of  fermentation.  With  true  scientific 
instinct  he  closed  with  the  conception  that  ferments 
are,  in  all  cases,  living  things,  and  that  the  substances 
formerly  regarded  as  ferments  are,  in  reality,  the 
food  of  the  ferments.  Touched  by  this  wand,  difn- 


INTRODUCTION.  xxili 

enlties  fell  rapidly  before  him.  He  proved  the  ferment 
of  lactic  acid  to  be  an  organism  of  a  certain  kind. 
The  ferment  of  butyric  acid  he  proved  to  be  an 
organism  of  a  different  kind.  He  was  soon  led  to  the 
fundamental  conclusion  that  the  capacity  of  an  organ- 
ism to  act  as  a  ferment  depended  on  its  power  to  live 
without  air.  The  fermentation  of  beer  was  sufficient 
to  suggest  this  idea.  The  yeast-plant,  like  many  others, 
can  live  either  with  or  without  free  air.  It  flourishes 
best  in  contact  with  free  air,  for  it  is  then  spared 
the  labour  of  wresting  from  the  malt  the  oxygen 
required  for  its  sustenance.  Supplied  with  free  air, 
however,  it  practically  ceases  to  be  a  ferment ;  while 
in  the  brewing  vat,  where  the  work  of  fermentation 
is  active,  the  budding  torula  is  completely  cut  off  by 
the  sides  of  the  vessel,  and  by  a  deep  layer  of  carbonic 
acid  gas,  from  all  contact  with  air.  The  butyric  fer- 
ment not  only  lives  without  air,  but  Pasteur  showed 
that  air  is  fatal  to  it.  He  finally  divided  microscopic 
organisms  into  two  great  classes,  which  he  named 
respectively  eerobies  and  anarobies,  the  former  requir- 
ing free  oxygen  to  maintain  life,  the  latter  capable  of 
living  without  free  oxygen,  but  able  to  wrest  this 
element  from  its  combinations  with  other  elements. 
This  destruction  of  pre-existing  compounds  and  forma- 
tion of  new  ones,  caused  by  the  increase  and  multipli- 
cation of  the  organism,  constitute  the  process  of 
fermentation. 


XXIV  INTRODUCTION. 

Under  this  head  are  also  rightly  ranked  the  phe- 
nomena of  putrefaction.  As  M.  Eadot  well  expresses 
it,  the  fermentation  of  sugar  may  be  described  as  the 
putrefaction  of  sugar.  In  this  particular  field  M. 
Pasteur,  whose  contributions  to  the  subject  are  of  the 
highest  value,  was  preceded  by  Schwann,  a  man  of 
great  merit,  of  whom  the  world  has  heard  too  little.1 
Schwann  placed  decoctions  of  meat  in  flasks,  sterilised 
the  decoctions  by  boiling,  and  then  supplied  them  with 
calcined  air,  the  power  of  which  to  support  life  he 
showed  to  be  unimpaired.  Under  these  circumstances 
putrefaction  never  set  in.  Hence  the  conclusion  of 
Schwann,  that  putrefaction  was  not  due  to  the  contact 
of  air,  as  affirmed  by  Gay-Lussac,  but  to  something 
suspended  in  the  air  which  heat  was  able  to  destroy. 
This  something  consists  of  living  organisms  which 
nourish  themselves  at  the  expense  of  the  organic 
substance,  and  cause  its  putrefaction. 

The  grasp  of  Pasteur  on  this  class  of  subjects 
was  embracing.  He  studied  acetic  fermentation,  and 
found  it  to  be  the  work  of  a  minute  fungus,  the  my- 
coderma  aceti,  which,  requiring  free  oxygen  for  its 
nutrition,  overspreads  the  surface  of  the  fermenting 
liquid.  By  the  alcoholic  ferment  the  sugar  of  the 
grape -juice  is  transformed  into  carbonic  acid  gas  and 

1  It  was  late  in  the  day  when  the  Royal  Society  made  him  a 
foreign  member. 


INTRODUCTION.  XXV 

alcohol,  the  former  exhaling,  the  latter  remaining  in 
the  wine.  By  the  mycoderma  aceti  the  wine  is,  in  its 
turn,  converted  into  vinegar.  Of  the  experiments  made 
in  connection  with  this  subject  one  deserves  especial 
mention.  It  is  that  in  which  Pasteur  suppressed  all 
albuminous  matters,  and  carried  on  the  fermentation 
with  purely  crystallisable  substances.  He  studied  the 
deterioration  of  vinegar,  revealed  its  cause,  and  the 
means  of  preventing  it.  He  denned  the  part  played 
by  the  little  eel- like  organisms  which  sometimes  swarm 
in  vinegar  casks,  and  ended  by  introducing  important 
ameliorations  and  improvements  in  the  manufacture  of 
vinegar.  The  discussion  with  Liebig  and  other  minor 
discussions  of  a  similar  nature,  which  M.  Kadot  has 
somewhat  strongly  emphasized,  I  will  not  here  dwell 
upon. 

It  was  impossible  for  an  inquirer  like  Pasteur  to 
evade  the  question — Whence  come  these  minute 
organisms  which  are  demonstrably  capable  of  pro- 
ducing effects  on  which  vast  industries  are  built  and 
on  which  whole  populations  depend  for  occupation 
and  sustenance  ?  He  thus  found  himself  face  to  face 
with  the  question  of  spontaneous  generation,  to  which 
the  researches  of  Pouchet  had  just  given  fresh  interest. 
Trained  as  Pasteur  was  in  the  experimental  sciences, 
he  had  an  immense  advantage  over  Pouchet,  whose 

culture  was  derived  from  the  sciences  of  observation. 

2 


XXVI  INTRODUCTION. 

One  by  one  the  statements  and  experiments  of  Pouchet 
were  explained  or  overthrown,  and  the  doctrine  of 
spontaneous  generation  remained  discredited  until  it 
was  revived  with  ardour,  ability,  and,  for  a  time,  with 
success,  by  Dr.  Bastian. 

A  remark  of  M.  Eadot's  on  page  103  needs  some 
qualification.  '  The  great  interest  of  Pasteur's  method 
consists,'  he  says,  '  in  its  proving  unanswerably  that 
the  origin  of  life  in  infusions  which  have  been  heated 
to  the  boiling  point  is  solely  due  to  the  solid  particles 
suspended  in  the  air.'  This  means  that  living  germs 
cannot  exist  in  the  liquid  when  once  raised  to  a  tem- 
perature of  212°  Fahr.  No  doubt  a  great  number  of 
organisms  collapse  at  this  temperature  ;  some  indeed, 
as  M.  Pasteur  has  shown,  are  destroyed  at  a  tempera- 
ture 90°  below  the  boiling  point.  But  this  is  by  no 
means  universally  the  case.  The  spores  of  the  hay- 
bacillus,  for  example,  have,  in  numerous  instances,  suc- 
cessfully resisted  the  boiling  temperature  for  one,  two, 
three,  four  hours ;  while  in  one  instance  eight  hours' 
continuous  boiling  failed  to  sterilise  an  infusion  of 
desiccated  hay.  The  knowledge  of  this  fact  caused 
me  a  little  anxiety  some  years  ago  when  a  meeting  was 
projected  between  M.  Pasteur  and  Dr.  Bastian.  For 
though,  in  regard  to  the  main  question,  I  knew  that 
the  upholder  of  spontaneous  generation  could  not  win, 
on  the  particular  issue  touching  the  death  temperature 
he  might  have  come  off  victor. 


INTRODUCTION.  XXvii 

The  manufacture  and  maladies  of  wine  next 
occupied  Pasteur's  attention.  He  had,  in  fact,  got 
the  key  to  this  whole  series  of  problems,  and  he  knew 
how  to  use  it.  Each  of  the  disorders  of  wine  was 
traced  to  its  specific  organism,  which,  acting  as  a 
ferment,  produced  substances  the  reverse  of  agreeable 
to  the  palate.  By  the  simplest  of  devices,  Pasteur,  at 
a  stroke,  abolished  the  causes  of  wine  disease.  Fortu- 
nately the  foreign  organisms  which,  if  unchecked, 
destroy  the  best  red  wines  are  extremely  sensitive  to 
heat.  A  temperature  of  50°  Cent.  (122°  Fahr.)  suffices 
to  kill  them.  Bottled  wines  once  raised  to  this  tem- 
perature, for  a  single  minute,  are  secured  from  subse- 
quent deterioration.  The  wines  suffer  in  no  degree 
from  exposure  to  this  temperature.  The  manner  in 
which  Pasteur  proved  this,  by  invoking  the  judgment 
of  the  wine-tasters  of  Paris,  is  as  amusing  as  it  is 
interesting. 

Moved  by  the  entreaty  of  his  master,  the  illustrious 
Dumas,  Pasteur  took  up  the  investigation  of  the 
diseases  of  silkworms  at  a  time  when  the  silk-husbandry 
of  France  was  in  a  state  of  ruin.  In  doing  so  he  did 
not,  as  might  appear,  entirely  forsake  his  former  line 
of  research.  Previous  investigators  had  got  so  far  as 
to  discover  vibratory  corpuscles  in  the  blood  of  the 
diseased  worms,  and  with  such  corpuscles  Pasteur  had 
already  made  himself  intimately  acquainted.  He  was 


XXviii  INTRODUCTION. 

therefore  to  some  extent  at  home  in  this  new  investi- 
gation.    The  calamity  was  appalling,  all  the  efforts 
made  to  stay  the  plague  having  proved  futile.     In 
June  1865  Pasteur  betook  himself  to  the  scene  of  the 
epidemic,  and  at  once  commenced  his  observations. 
On  the  evening  of  his  arrival  he  had  already  discovered 
the  corpuscles,  and  shown  them  to  others.     Acquainted 
as  he  was  with  the  work  of  living  ferments,  his  mind 
was  prepared  to  see  in  the  corpuscles  the  cause  of  the 
epidemic.     He  followed  them  through  all  the  phases 
of  the  insect's  life — through  the  eggs,  through  the 
worm,  through  the  chrysalis,  through  the  moth.     He 
proved  that  the  germ  of  the  malady  might  be  present 
in  the  eggs  and  escape  detection.     In  the  worm  also 
it  might  elude  microscopic  examination.     But  in  the 
moth  it  reached  a  development  so  distinct  as  to  ren- 
der its  recognition  immediate.     From  healthy  moths 
healthy  eggs  were  sure  to  spring ;  from  healthy  eggs 
healthy  worms ;  from  healthy  worms  fine  cocoons  :  so 
that  the  problem  of  the  restoration  to  France  of  its 
silk-husbandry  reduced  itself  to  the  separation  of  the 
healthy  from  the  unhealthy  moths,  the  rejection  of 
the  latter,  and  the  exclusive  employment  of  the  eggs 
of  the  former.     M.  Eadot  describes  how  this  is  now 
done  on  the  largest  scale,  with  the  most  satisfactory 
results. 

The  bearing  of  this  investigation  on  the  parasitic 
theory  of  communicable  diseases  was  thus  illustrated  : 


INTEODUCTION. 

Worms  were  infected  by  permitting  them  to  feed  for 
a  single  meal  on  leaves  over  which  corpusculous 
matter  had  been  spread;  they  were  infected  by  in- 
oculation, and  it  was  shown  how  they  infected  each 
other  by  the  wounds  and  scratches  of  their  own  claws. 
By  the  association  of  healthy  with  diseased  worms, 
the  infection  was  communicated  to  the  former.  In- 
fection at  a  distance  was  also  produced  by  the  wafting 
of  the  corpuscles  through  the  air.  The  various  modes 
in  which  communicable  diseases  are  diffused  among 
human  populations  were  illustrated  by  Pasteur's 
treatment  of  the  silkworms.  '  It  was  no  hypothetical, 
infected  medium — no  problematical  pythogenic  gas — 
that  killed  the  worms.  It  was  a  definite  organism.' l 
The  disease  thus  far  described  is  that  called  pebrine, 
-which  was  the  principal  scourge  at  the  time.  Another 
formidable  malady  was  also  prevalent,  called  flacherie, 
the  cause  of  which,  and  the  mode  of  dealing  with  it, 
were  also  pointed  out  by  Pasteur. 

Overstrained  by  years  of  labour  in  this  field, 
Pasteur  was  smitten  with  paralysis  in  October  1868. 
But  this  calamity  did  not  prevent  him  from  making 
a  journey  to  Alais  in  January  1869,  for  the  express 
purpose  of  combating  the  criticisms  to  which  his 
labours  had  been  subjected.  Pasteur  is  combustible, 
and  contradiction  readily  stirs  him  into  flame.  No 

1  These  words  were  uttered  at  a  time  when  the  pythogenic  theory 
was  more  in  favour  than  it  is  now. 


XXX  INTRODUCTION. 

scientific  man  now  living  has  fought  so  many  battles 
as  he.  To  enable  him  to  render  his  experiments 
decisive,  the  French  Emperor  placed  a  villa  at  his  dis- 
posal near  Trieste,  where  silkworm  culture  had  been 
carried  on  for  some  time  at  a  loss.  The  success  here 
is  described  as  marvellous ;  the  sale  of  cocoons  giving 
to  the  villa  a  net  profit  of  twenty-six  millions  of  francs.1 
From  the  Imperial  villa  M.  Pasteur  addressed  to  me 
a  letter,  a  portion  of  which  I  have  already  published. 
It  may  perhaps  prove  usefully  suggestive  to  our  Indian 
or  Colonial  authorities  if  I  reproduce  it  here  : — 

'  Permettez-moi  de  terminer  ces  quelques  lignes  que 
je  dois  dieter,  vaincu  que  je  suis  par  la  maladie,  en 
vous  faisant  observer  que  vous  rendriez  service  aux 
Colonies  de  la  Grande-Bretagne  en  repandant  la  con- 
naissance  de  ce  livre,  et  des  principes  que  j'etablis 
touchant  la  maladie  des  vers  a  soie.  Beaucoup  de  ces 
colonies  pourraient  cultiver  le  murier  avec  succes,  et, 
en  jetant  les  yeux  sur  mon  ouvrage,  vous  vous  con- 
vaincrez  aisement  qu'il  est  facile  aujourd'hui,  non- 
seulement  d'eloigner  la  maladie  regnante,  mais  en 
outre  de  donner  aux  recoltes  de  la  soie  une  prosperite 
qu'elles  n'ont  jamais  eue.' 

The  studies  on  wine  prepare  us  for  the  '  Studies 
on  Beer,'  which  followed  the  investigation  of  silkworm 

1  The  work   on  Diseases   of  Silkworms   was   dedicated   to   the 
Empress  of  the  French. 


INTRODUCTION.  XXXI 

diseases.     The  sourness,  putridity,  and  other  maladies 
of  beer  Pasteur  traced  to  special  '  ferments  of  disease,' 
of  a  totally  different  form,  and  therefore  easily  dis- 
tinguished from  the  true  torula  or  yeast-plant.     Many 
mysteries  of  our  breweries  were  cleared  up  by  this 
inquiry.      Without  knowing   the    cause,  the  brewer 
not  unfrequently  incurred  heavy  losses  through  the 
use  of  bad  yeast.     Five  minutes'  examination  with  the 
microscope  would  have  revealed  to  him  the  cause  of 
the  badness,  and  prevented  him  from  using  the  yeast. 
He  would  have  seen  the  true  torula  overpowered  by 
foreign  intruders.     The  microscope  is,  I  believe,  now 
everywhere  in  use.     At  Burton-on- Trent  its  aid  was 
very  soon  invoked.     At  the  conclusion  of  his  studies 
on  beer  M.  Pasteur  came  to  London,  where  I  had  the 
pleasure  of  conversing  with  him.     Crippled  by  paraly- 
sis, bowed  down  by  the  sufferings   of    France,    and 
anxious  about  his  family  at  a  troubled  and  an  un- 
certain time,  he  appeared  low  in  health  and  depressed 
in  spirits.     His  robust  appearance  when   he   visited 
London,  on  the  occasion  of  the  Edinburgh  Anniver- 
sary, was  in  marked  and  pleasing  contrast  with  my 
memory  of  his  aspect  at  the  time  to  which  I  have 
referred. 

While  these  researches  were  going  on,  the  Germ 
Theory  of  infectious  disease  was  noised  abroad.  The 
researches  of  Pasteur  were  frequently  referred  to  as 


XXX11  INTRODUCTION. 

bearing  upon  the  subject,  though  Pasteur  himself 
kept  clear  for  a  long  time  of  this  special  field  of  in- 
quiry. He  was  not  a  physician,  and  he  did  not  feel 
called  upon  to  trench  upon  the  physician's  domain. 
And  now  I  would  beg  of  him  to  correct  me  if,  at  this 
point  of  the  Introduction,  I  should  be  betrayed  into 
any  statement  that  is  not  strictly  correct. 

In  1876  the  eminent  microscopist,  Professor  Cohn 
of  Breslau,  was  in  London,  and  he  then  handed  me 
a  number  of  his  '  Beitrage,'  containing  a  memoir 
by  Dr.  Koch  on  Splenic  Fever  (Milzbrand,  Charbon, 
Malignant  Pustule),  which  seemed  to  me  to  mark  an 
epoch  in  the  history  of  this  formidable  disease.  With 
admirable  patience,  skill,  and  penetration,  Koch  fol- 
lowed up  the  life  history  of  bacillus  anthracis,  the  con- 
tagium  of  this  fever.  At  the  time  here  referred  to  he 
was  a  young  physician  holding  a  small  appointment 
in  the  neighbourhood  of  Breslau,  and  it  was  easy  to 
predict,  as  I  predicted  at  the  time,  that  he  would  soon 
find  himself  in  a  higher  position.  When  I  next  heard 
of  him  he  was  head  of  the  Imperial  Sanitary  Institute 
of  Berlin.  Koch's  recent  history  is  pretty  well  known 
in  England,  while  his  appreciation  by  the  German 
Government  is  shown  by  the  rewards  and  honours 
lately  conferred  upon  him. 

Koch  was  not  the  discoverer  of  the  parasite  of 
splenic  fever.  Davaine  and  Eayer,  in  1850,  had  ob- 
served the  little  microscopic  rods  in  the  blood  of 


INTRODUCTION.  XXXlii 

animals  which  had  died  of  splenic  fever.  But  they 
were  quite  unconscious  of  the  significance  of  their 
observation,  and  for  thirteen  years,  as  M.  Eadot  informs 
us,  strangely  let  the  matter  drop.  In  1863  Davaine's 
attention  was  again  directed  to  the  subject  by  the 
researches  of  Pasteur,  and  he  then  pronounced  the 
parasite  to  be  the  cause  of  the  fever.  He  was  opposed 
by  some  of  his  fellow-countrymen ;  long  discussions 
followed,  and  a  second  period  of  thirteen  years,  ending 
with  the  publication  of  Koch's  paper,  elapsed,  before 
M.  Pasteur  took  up  the  question.  I  always,  indeed, 
assumed  that  from  the  paper  of  the  learned  German 
came  the  impulse  towards  a  line  of  inquiry  in  which 
M.  Pasteur  has  achieved  such  splendid  results.  Things 
presenting  themselves  thus  to  my  mind,  M.  Radot 
will,  I  trust,  forgive  me  if  I  say  that  it  was  with 
very  great  regret  that  I  perused  the  disparaging 
references  to  Dr.  Koch  which  occur  in  the  chapter 
on  splenic  fever. 

After  Koch's  investigation,  no  doubt  could  be  en- 
tertained of  the  parasitic  origin  of  this  disease.  It 
completely  cleared  up  the  perplexity  previously  existing 
as  to  the  two  forms — the  one  fugitive,  the  other  per- 
manent— hi  which  the  contagium  presented  itself.  I 
may  say  that  it  was  on  the  conversion  of  the  per- 
manent hardy  form  into  the  fugitive  and  sensitive  one, 
in  the  case  of  bacillus  subtilis  and  other  organisms,  that 
the  method  of  sterilising  by  '  discontinuous  heating  ' 


XXXIV  INTKODUCTION. 

introduced  by  me  in  February  1877  was  founded.  The 
difference  between  an  organism  and  its  spores,  in  point 
of  durability,  had  not  escaped  the  penetration  of 
Pasteur.  This  difference  Koch  showed  to  be  of  para- 
mount importance  in  splenic  fever.  He,  moreover, 
proved  that  while  mice  and  guinea-pigs  were  infallibly 
killed  by  the  parasite,  birds  were  able  to  defy  it. 

And  here  we  come  upon  what  may  be  called  a  hand- 
specimen  of  the  genius  of  Pasteur,  which  strikingly 
illustrates  its  quality.  Why  should  birds  enjoy  the 
immunity  established  by  the  experiments  of  Koch  ? 
Here  is  the  answer.  The  temperature  which  prohibits 
the  multiplication  of  bacillus  anthracis  in  infusions  is 
44°  Cent.  (111°  Fahr.).  The  temperature  of  the  blood 
of  birds  is  from  41°  to  42°.  It  is  therefore  close  to 
the  prohibitory  temperature.  But  then  the  blood 
globules  of  a  living  fowl  are  sure  to  offer  a  certain 
resistance  to  any  attempt  to  deprive  them  of  their 
oxygen — a  resistance  not  experienced  in  an  infusion. 
May  not  this  resistance,  added  to  the  high  tempera- 
ture of  the  fowl,  suffice  to  place  it  beyond  the  power 
of  the  parasite  ?  Experiment  alone  could  answer 
this  question,  and  Pasteur  made  the  experiment. 
By  placing  its  feet  in  cold  water  he  lowered  the  tem- 
perature of  a  fowl  to  37°  or  38°.  He  inoculated 
the  fowl,  thus  chilled,  with  the  splenic  fever  parasite, 
and  in  twenty- four  hours  it  was  dead.  The  argu- 
ment was  clinched  by  inoculating  a  chilled  fowl,  per- 


INTRODUCTION.  XXXV 

mitting  the  fever  to  come  to  a  head,  and  then  remov- 
ing the  fowl,  wrapped  in  cotton-wool,  to  a  chamber 
with  a  temperature  of  35°.  The  strength  of  the 
patient  returned  as  the  career  of  the  parasite  was 
brought  to  an  end,  and  in  a  few  hours  health  was 
restored.  The  sharpness  of  the  reasoning  here  is 
only  equalled  by  the  conclusiveness  of  the  experiment, 
which  is  full  of  suggestiveness  as  regards  the  treat- 
ment of  fevers  in  man. 

Pasteur  had  little  difficulty  in  establishing  the 
parasitic  origin  of  fowl  cholera ;  indeed,  the  parasite 
had  been  observed  by  others  before  him.  But  by  his 
successive  cultivations,  he  rendered  the  solution  sure. 
His  next  step  will  remain  for  ever  memorable  in  the 
history  of  medicine.  I  allude  to  what  he  calls  '  virus 
attenuation.'  And  here  it  may  be  well  to  throw  out 
a  few  remarks  in  advance.  When  a  tree,  or  a  bundle 
of  wheat  or  barley  straw,  is  burnt,  a  certain  amount  of 
mineral  matter  remains  in  the  ashes — extremely  small 
in  comparison  with  the  bulk  of  the  tree  or  of  the  straw, 
but  absolutely  essential  to  its  growth.  In  a  soil  lacking, 
or  exhausted  of,  the  necessary  mineral  constituents,  the 
tree  cannot  live,  the  crop  cannot  grow.  Now  contagia 
are  living  things,  which  demand  certain  elements  of  life 
just  as  inexorably  as  trees,  or  wheat,  or  barley ;  and  it 
is  not  difficult  to  see  that  a  crop  of  a  given  parasite  may 
so  far  use  up  a  constituent  existing  in  small  quantities 


XXXVI  INTRODUCTION. 

in  the  body,  but  essential  to  the  growth  of  the  parasite, 
as  to  render  the  body  unfit  for  the  production  of  a 
second  crop.  The  soil  is  exhausted,  and,  until  the 
lost  constituent  is  restored,  the  body  is  protected 
from  any  further  attack  of  the  same  disorder.  Such 
an  explanation  of  non-recurrent  diseases  naturally 
presents  itself  to  a  thorough  believer  in  the  germ 
theory,  and  such  was  the  solution  which,  in  reply  to 
a  question,  I  ventured  to  offer  nearly  fifteen  years 
ago  to  an  eminent  London  physician.  To  exhaust  a 
soil,  however,  a  parasite  less  vigorous  and  destructive 
than  the  really  virulent  one  may  suffice ;  and  if,  after 
having  by  means  of  a  feebler  organism  exhausted  the 
soil,  without  fatal  result,  the  most  highly  virulent 
parasite  be  introduced  into  the  system,  it  will  prove 
powerless.  This,  in  the  language  of  the  germ  theory, 
is  the  whole  secret  of  vaccination. 

The  general  problem,  of  which  Jenner  s  discovery 
was  a  particular  case,  has  been  grasped  by  Pasteur,  in 
a  manner,  and  with  results,  which  five  short  years  ago 
were  simply  unimaginable.  How  much  '  accident ' 
had  to  do  with  shaping  the  course  of  his  enquiries 
I  know  not.  A  mind  like  his  resembles  a  photo- 
graphic plate,  which  is  ready  to  accept  and  develop 
luminous  impressions,  sought  and  unsought.  In  the 
chapter  on  fowl  cholera  is  described  how  Pasteur  first 
obtained  his  attenuated  virus.  By  successive  cultiva- 
tions of  the  parasite  he  showed,  that  after  it  had  been 


INTRODUCTION.  XXXvii 

a  hundred  times  reproduced,  it  continued  to  be  as 
,  virulent  as  at  first.  One  necessary  condition  was, 
however,  to  be  observed.  It  was  essential  that  the 
cultures  should  rapidly  succeed  each  other — that  the 
organism,  before  its  transference  to  a  fresh  cultivating 
liquid,  should  not  be  left  long  in  contact  with  air. 
"When  exposed  to  air  for  a  considerable  time  the  virus 
becomes  so  enfeebled  that  when  fowls  are  inoculated 
with  it,  though  they  sicken  for  a  time,  they  do  not 
die.  But  this  '  attenuated '  virus,  which  M.  Radot 
justly  calls  'benign,'  constitutes  a  sure  protection 
against  the  virulent  virus.  It  so  exhausts  the  soil 
that  the  really  fatal  contagium  fails  to  find  there  the 
elements  necessary  to  its  reproduction  and  multipli- 
cation. 

Pasteur  affirms  that  it  is  the  oxygen  of  the  air 
which,  by  lengthened  contact,  weakens  the  virus  and 
converts  it  into  a  true  vaccine.  He  has  also  weakened 
it  by  transmission  through  various  animals.  It  was 
this  form  of  attenuation  that  was  brought  into  play 
in  the  case  of  Jenner. 

The  secret  of  attenuation  had  thus  become  an  open 
one  to  Pasteur.  He  laid  hold  of  the  murderous  virus 
of  splenic  fever,  and  succeeded  in  rendering  it,  not 
only  harmless  to  life,  but  a  sure  protection  against  the 
virus  in  its  most  concentrated  form.  No  man,  in  my 
opinion,  can  work  at  these  subjects  so  rapidly  as 
Pasteur  without  falling  into  errors  of  detail.  But  this 


XXXV111  INTRODUCTION. 

may  occur  while  his  main  position  remains  impreg- 
nable. Such  a  result,  for  example,  as  that  obtained 
in  presence  of  so  many  witnesses  at  Melun  must 
surely  remain  an  ever-memorable  conquest  of  science. 
Having  prepared  his  attenuated  virus,  and  proved,  by 
laboratory  experiments,  its  efficacy  as  a  protective 
vaccine,  Pasteur  accepted  an  invitation  from  the 
President  of  the  Society  of  Agriculture  at  Melun,  to 
make  a  public  experiment  on  what  might  be  called  an 
agricultural  scale.  This  act  of  Pasteur's  is,  perhaps, 
the  boldest  thing  recorded  in  this  book.  It  naturally 
caused  anxiety  among  his  colleagues  of  the  Academy, 
who  feared  that  he  had  been  rash  in  closing  with  the 
proposal  of  the  President. 

But  the  experiment  was  made.  A  flock  of  sheep 
was  divided  into  two  groups,  the  members  of  one  group 
being  all  vaccinated  with  the  attenuated  virus,  while 
those  of  the  other  group  were  left  unvaccinated  A 
number  of  cows  were  also  subjected  to  a  precisely 
similar  treatment.  Fourteen  days  afterwards,  all  the 
sheep  and  all  the  cows,  vaccinated  and  unvaccinated, 
were  inoculated  with  a  very  virulent  virus ;  and  three 
days  subsequently  more  than  two  hundred  persons 
assembled  to  witness  the  result.  The  '  shout  of 
admiration,'  mentioned  by  M.  Eadot,  was  a  natural 
outburst  under  the  circumstances.  Of  twenty-five 
sheep  which  had  not  been  protected  by  vaccination, 
twenty-one  were  already  dead,  and  the  remaining  ones 


INTRODUCTION.  XXxix 

were  dying.  The  twenty-five  vaccinated  sheep,  on 
the  contrary,  were  '  in  full  health  and  gaiety.'  In  the 
unvaccinated  cows  intense  fever  was  produced,  while 
the  prostration  was  so  great  that  they  were  "unable 
to  eat.  Tumours  were  also  formed  at  the  points  of 
inoculation.  In  the  vaccinated  cows  no  tumours  were 
formed  ;  they  exhibited  no  fever,  nor  even  an  elevation 
of  temperature,  while  their  power  of  feeding  was 
unimpaired.  No  wonder  that  '  breeders  of  cattle  over- 
whelmed Pasteur  with  applications  for  vaccine.'  At 
the  end  of  1881  close  upon  34,000  animals  had  been 
vaccinated,  while  the  number  rose  in  1883  to  nearly 
500,000. 

M.  Pasteur  is  now  exactly  sixty-two  years  of 
age ;  but  his  energy  is  unabated.  At  the  end  of 
this  volume  we  are  informed  that  he  has  already 
taken  up  and  examined  with  success,  as  far  as  his 
experiments  have  reached,  the  terrible  and  mysterious 
disease  of  rabies  or  hydrophobia.  Those  who  hold  all 
communicable  diseases  to  be  of  parasitic  origin,  in- 
clude, of  course,  rabies  among  the  number  of  those 
produced  and  propagated  by  a  living  contagium.  From 
his  first  contact  with  the  disease  Pasteur  showed  his 
accustomed  penetration.  If  we  see  a  man  mad,  we  at 
once  refer  his  madness  to  the  state  of  his  brain.  It  is 
somewhat  singular  that  in  the  face  of  this  fact  the 
virus  of  a  mad  dog  should  be  referred  to  the  animal's 


xl  INTRODUCTION. 

saliva.  The  saliva  is,  no  doubt,  infected,  but  Pasteur 
soon  proved  the  real  seat  and  empire  of  the  disorder 
to  be  the  nervous  system. 

The  parasite  of  rabies  had  not  been  securely 
isolated  when  M.  Eadot  finished  his  task.  But  last 
May,  at  the  instance  of  M.  Pasteur,  a  commission 
was  appointed  by  the  Minister  of  Public  Instruction 
in  France,  to  examine  and  report  upon  the  results 
which  he  had  up  to  that  time  obtained.  A  preliminary 
report,  issued  to  appease  public  impatience,  reached 
me  before  I  quitted  Switzerland  this  year.  It  inspires 
the  sure  and  certain  hope  that,  as  regards  the  attenu- 
ation of  the  rabic  virus,  and  the  rendering  of  an 
animal,  by  inoculation,  proof  against  attack,  the 
success  of  M.  Pasteur  is  assured.  The  commission, 
though  hitherto  extremely  active,  is  far  from  the  end 
of  its  labours ;  but  the  results  obtained  so  far  may 
be  thus  summed  up  : — 

Of  six  dogs  unprotected  by  vaccination,  three 
succumbed  to  the  bites  of  a  dog  in  a  furious  state  of 
madness. 

Of  eight  unvaccinated  dogs,  six  succumbed  to  the 
intravenous  inoculation  of  rabic  matter. 

Of  five  unvaccinated  dogs,  all  succumbed  to  inocu- 
lation, by  trepanning,  of  the  brain. 

Finally,  of  three-and-twenty  vaccinated  dogs,  not 
one  was  attacked  with  the  disease  subsequent  to 
inoculation  with  the  most  potent  virus. 


INTRODUCTION.  xli 

Surely  results  such  as  those  recorded  in  this 
book  are  calculated,  not  only  to  arouse  public 
interest,  but  public  hope  and  wonder.  Never  before, 
during  the  long  period  of  its  history,  did  a  day  like 
the  present  dawn  upon  the  science  and  art  of  medi- 
cine. Indeed,  previous  to  the  discoveries  of  recent 
times,  medicine  was  not  a  science,  but  a  collection  of 
empirical  rules  dependent  for  their  interpretation  and 
application  upon  the  sagacity  of  the  physician.  How 
does  England  stand  in  relation  to  the  great  work  now 
going  on  around  her  ?  She  is,  and  must  be,  behind- 
hand. Scientific  chauvinism  is  not  beautiful  in 
my  eyes.  Still  one  can  hardly  see,  without  depreca- 
tion and  protest,  the  English  investigator  handicapped 
in  so  great  a  race  by  short  sighted  and  mischievous 
legislation. 

A  great  scientific  theory  has  never  been  accepted 
without  opposition.  The  theory  of  gravitation,  the 
theory  of  undulation,  the  theory  of  evolution,  the 
dynamical  theory  of  heat — all  had  to  push  their  way 
through  conflict  to  victory.  And  so  it  has  been  with 
the  Germ  Theory  of  communicable  diseases.  Some 
outlying  members  of  the  medical  profession  dispute 
it  still.  I  am  told  they  even  dispute  the  communica- 
bility  of  cholera.  Such  must  always  be  the  course  of 
things,  as  long  as  men  are  endowed  with  different 
degrees  of  insight.  Where  the  mind  of  genius  dis- 
cerns the  distant  truth,  which  it  pursues,  the  mind 


xlii  INTRODUCTION. 

not  so  gifted  often  discerns  nothing  but  the  extra- 
vagance, which  it  avoids.  Names,  not  yet  forgotten, 
could  be  given  to  illustrate  these  two  classes  of  minds. 
As  representative  of  the  first  class,  I  would  name  a 
man  whom  I  have  often  named  before,  who,  basing 
himself  in  great  part  on  the  researches  of  Pasteur, 
fought,  in  England,  the  battle  of  the  germ  theory  with 
persistent  valour,  but  whose  labours  broke  him  down 
before  he  saw  the  triumph  which  he  /oresaw  completed. 
Many  of  my  medical  friends  will  understand  that  I 
allude  here  to  the  late  Dr.  William  Budd,  of  Bristol. 

The  task  expected  of  me  is  now  accomplished,  and 
the  reader  is  here  presented  with  a  record,  in  which 
the  verities  of  science  are  endowed  with  the  interest 
of  romance. 

JOHN   TYNDALL. 

ROYAL  INSTITUTION  :  December  1884 


RECOLLECTIONS  OF  CHILDHOOD  AND 
YOUTH. 

FIRST    DISCOVEEIES. 

*  COME,  M.  Pasteur !  you  must  shake  off  the  demon 
of  idleness  ! '  It  was  the  night  watcher  of  the  College 
of  Besan9on,  who  invariably  at  four  o'clock  in  the 
morning  entered  Pasteur's  room  and  roused  him  with 
this  vigorous  salute,  which  was  accompanied,  when 
necessary,  by  a  sound  shaking.  Pasteur  was  then 
eighteen  years  of  age.  In  addition  to  his  food  and 
lodging,  the  royal  college  paid  him  twenty-four  francs 
a  month.  But  if  his  place  was  a  modest  one,  it  suf- 
ficed at  the  time  for  his  ambition  :  it  was  the  first  tie 
which  bound  him  to  the  University. 

'  Ah,'  said  his  father  to  him  frequently,  '  if  only 
you  could  become  some  day  professor  in  the  College 
of  Arbois  I  should  be  the  happiest  man  on  earth.' 

Already,  when  he  resided  at  Dole,  and  when  his 
son  was  not  yet  two  years  old,  this  father  permitted 
himself  to  dream  thus  of  the  future.  What  would  he 


2  LOUIS  PASTEUR. 

have  said  had  it  been  announced  to  him  that  fifty- 
eight  years  later,  on  the  fa9ade  of  the  little  house  in 
the  Rue  des  Tanneurs,  would  be  placed,  in  the  pre- 
sence of  his  living  son — laden  with  honours,  laden  with 
glory,  passing  in  the  midst  of  a  triumphal  procession 
along  the  paved  town — a  plate  bearing  these  words  hi 
letters  of  gold : 

HEKE  WAS  BOEN  Louis  PASTEUR, 
December  27,  1822. 

Pausing  before  this  house,  Pasteur  recalled  the 
image  of  his  father  and  mother — of  those  whom  he 
called  his  dear  departed  ones — and  from  the  far-off 
depths  of  his  childhood  came  so  many  memories  of 
affection,  devotion,  and  paternal  sacrifices  that  he 
burst  into  tears. 

The  life  of  his  father  had  been  a  rough  one.  An 
old  soldier,  decorated  on  the  field  of  battle,  on  return- 
ing to  France,  where  he  had  no  longer  a  home,  he 
was  obliged  to  work  hard  to  earn  his  bread.  He  took 
up  the  trade  of  a  tanner.  Soon  afterwards,  having 
made  the  acquaintance  of  a  worthy  young  girl,  he 
joined  his  lot  with  hers,  and  together  they  entered 
courageously  on  the  labours  of  their  married  life — 
he  calm,  reflective,  and  more  eager,  whenever  he  had 
a  moment  of  repose,  for  the  society  of  books  than  for 
the  society  of  his  neighbours;  she  full  of  enthusiasm, 
her  heart  and  spirit  agitated  by  thoughts  above  the 


KECOLLECTIONS  OF  CHILDHOOD  AND  YOUTH.        3 

level  of  her  modest  life.  Both  of  them  watched  with 
ceaseless  solitude  over  their  little  Louis,  of  whom, 
with  mingled  pride  and  tenderness,  they  used  to  say, 
'  We  will  make  of  him  an  educated  man.' 

In  1825  the  Pasteur  family  quitted  Dole  and  esta- 
blished themselves  at  Arbois,  where,  on  the  borders 
of  the  Cuisance,  the  father  of  our  hero  had  bought  a 
small  tanyard.  At  this  town,  and  in  this  yard,  Louis 
Pasteur  spent  his  childhood.  As  soon  as  he  was  old 
enough  to  be  received  as  a  half-pay  scholar  he  was 
sent  to  the  communal  college.  He,  the  smallest  of 
all  the  pupils,  was  so  proud  of  passing  under  the  great 
arched  doorway  of  this  ancient  establishment,  that 
he  arrived  laden  with  enormous  dictionaries,  of  which 
there  was  no  need. 

In  the  midst  of  his  laborious  occupations  the 
father  of  Pasteur  took  upon  himself  the  task  of  super- 
intending his  son's  lessons  every  evening.  This  was 
at  first  no  sinecure.  Louis  Pasteur  did  not  always 
take  the  shortest  road  either  to  reach  his  class  or  to 
return  to  his  work  at  home.  Some  old  friends  still 
living  remember  having  made  with  the  little  Pasteur 
fishing  parties,  which  proved  so  pleasant  that  they 
have  been  continued  to  the  present  day.  The  boy, 
moreover,  instead  of  applying  himself  to  his  lessons, 
often  escaped  and  amused  himself  by  making  large 
portraits  of  his  neighbours,  male  and  female.  A 
dozen  of  these  portraits  are  still  to  be  seen  in  the 


4  LOUIS  PASTEUR. 

houses  of  Arbois,  all  bearing  his  signature.  Consider- 
ing that  his  age  at  the  time  was  only  thirteen,  the 
accuracy  of  the  drawing  is  astonishing. 

'  What  a  pity,'  said  an  old  lady  of  Arbois  a  short 
time  since,  '  that  he  should  have  buried  himself  in 
chemistry  !  He  has  missed  his  vocation,  for  he  might 
by  this  time  have  made  his  reputation  as  a  painter.' 

It  was  not  until  he  reached  the  third  class  that 
Louis  Pasteur,  beginning  to  realise  the  sacrifices 
which  his  father  imposed  upon  himself,  determined  to 
abandon  his  fishing  implements  and  his  crayons,  feel- 
ing aroused  within  him  that  passion  for  work  which 
was  to  form  the  foundation  of  his  life.  The  Principal 
of  the  college,  who  followed  with  watchful  interest  the 
progress  of  a  pupil  who,  in  his  first  effort,  had  out- 
stripped all  his  comrades,  used  to  say,  'He  will  go 
far.  It  is  not  for  the  chair  of  a  small  college  like  ours 
that  we  must  prepare  him  ;  he  must  become  pro- 
fessor in  a  royal  college.  My  little  friend,'  he  would 
add,  '  think  of  the  great  Ecole  Normale.' 

The  College  of  Arbois  having  no  professor  of  philo- 
sophy, Pasteur  quitted  it  for  Besan9on.  There  he 
remained  for  the  scholars'  year,  received  the  degree  of 
bachelier  es  lettres,  and  was  immediately  appointed 
tutor  in  the  same  college.  In  the  intervals  of  his 
duties  he  followed  the  course  of  mathematics  neces- 
sary to  prepare  him  for  the  scientific  examinations  of 
the  Ecole  Normale.  He  must  have  been  already 


RECOLLECTIONS   OF   CHILDHOOD   AND   YOUTH.         5 

endowed  with  a  singular  maturity  of  character,  for 
the  director  confided  to  him  the  superintendence  of 
the  quarters  of  the  older  pupils,  who  during  class  time 
were  his  comrades.  In  the  class  room  his  table  was 
in  the  midst  of  them ;  and  never  had  so  young  a 
master  so  much  authority,  and  at  the  same  time  so 
little  need  for  its  exercise. 

His  first  taste  for  chemistry  manifested  itself  by 
frequent  questions  addressed  during  class  time  to  an 
old  professor  named  Darlay.  This  questioning  was 
so  often  repeated  that  the  good  man,  quite  bewildered, 
ended  by  declaring  that  it  was  for  him  to  interrogate 
Pasteur  and  not  for  Pasteur  to  interrogate  him.  His 
pupil  pressed  him  no  further,  but  having  heard  that  at 
Besan9on  there  lived  an  apothecary  who  had  once  dis- 
tinguished himself  by  a  paper  inserted  in  the  '  Annales 
de  Chimie  et  de  Physique,'  he  sought  this  man,  with  a 
view  of  ascertaining  whether,  on  holidays,  he  would 
consent  to  give  him  lessons  secretly. 

At  the  examination  for  the  Ecole  Normale,  Pasteur 
passed  as  fourteenth  in  the  list.  This  rank,  however, 
did  not  satisfy  him.  Notwithstanding  the  censure  of 
his  fellow  candidates  he  declared  that  he  would  begin  a 
new  year  of  preparation.  It  was  in  Paris  itself  that  he 
chose  to  work — in  one  of  the  silent  corners  of  the  city, 
amid  the  seclusion  of  preparatory  schools  and  convents. 

In  the  Impasse  des  Feuillantines,  there  lived  a 
schoolmaster,  M.  Barbet  by  name,  or  rather  le  pere 


6  LOUIS  PASTEUR. 

Barbet,  as  the  Franc-Comtois,  with  provincial  fami- 
liarity, used  to  call  him.  Pasteur  begged  to  be  allowed 
to  enter  his  institution,  not  as  an  assistant,  but  as 
a  simple  pupil.  Knowing  how  slender  were  the  means 
of  his  young  compatriot,  M.  Barbet  reduced  the  fees 
of  his  pupil  by  one-third.  Such  kindness  was  cus- 
tomary with  the  pere  Barbet,  who  did  not  like  to  be 
reminded  of  his  generosity.  This,  however,  gives 
double  pleasure  to  him  who  records  it. 

The  year  passes,  the  time  of  the  examination 
arrives,  and  Pasteur  is  received  as  fourth  on  the  list. 
Thus  at  last,  in  the  month  of  October  1843,  he  finds 
himself  in  that  Ecole  Normale  in  which  he  was 
destined  to  take  so  great  a  place.  Pasteur's  taste  for 
chemistry  had  become  a  passion  which  he  could  now 
satisfy  to  his  heart's  content.  Chemistry  was  at  this 
time  taught  at  the  Sorbonne  by  M.  Dumas  and  at  the 
Ecole  Normale  by  M.  Balard.  The  pupils  of  the  Ecole 
attended  both  courses  of  lectures.  Different  as  were 
the  two  professors,  both  of  them  exercised  great  influ- 
ence on  their  pupils.  M.  Dumas,  with  his  serene 
gravity  and  his  profound  respect  for  his  auditory, 
never  allowed  the  smallest  incorrectness  to  slip  into 
his  exposition.  M.  Balard,  with  a  vivacity  quite 
juvenile,  with  the  excitement  of  a  southerner  in  the 
tribune,  did  not  always  give  his  words  time  to  follow 
his  thoughts.  It  was  he  who  once,  showing  a  little 
potash  to  his  audience,  exclaimed  with  a  fervour  which 


RECOLLECTIONS  OF  CHILDHOOD  AND  YOUTH.        7 

has  become  celebrated,  'Potash,  which — potash,  then 
— potash,  in  short,  which  I  now  present  to  you.' 

The  general  principles  which  M.  Dumas  in  his 
teaching  delighted  to  develop,  the  multitude  of  facts 
which  M.  Balard  unfolded  to  his  pupils,  all  answered 
to  the  needs  of  Pasteur's  mind.  If  he  loved  the  vaster 
horizons  of  science,  he  was  also  possessed  by  the 
anxious  desire  for  exactitude,  and  for  the  perpetual 
control  of  experiment.  Each  of  the  lectures  of  the 
Ecole  Normale  and  of  the  Sorbonne  excited  in  him 
a  profound  enthusiasm.  One  day  M.  Dumas,  while 
illustrating  the  solidification  of  carbonic  acid,  begged 
for  the  loan  of  a  handkerchief  to  receive  the  carbonic 
acid  snow.  Pasteur  rushed  forward,  and,  presenting 
his  handkerchief,  received  the  snow.  He  returned 
triumphant,  and  running  forthwith  to  the  Ecole  Nor- 
male, repeated  the  principal  experiments  which  the 
illustrious  chemist  had  just  exhibited  to  his  audience. 
He  preserved  religiously  the  handkerchief  which  had 
been  touched  by  M.  Dumas. 

Pasteur  usually  spent  his  Sundays  with  M.  Bar- 
ruel,  the  assistant  of  M.  Dumas.  He  thought  of 
nothing  but  experiments.  For  a  long  time  in  one 
of  the  laboratories  of  the  Ecole  Normale  was  exhibited 
a  basin— perhaps  it  is  still  shpwn — containing  sixty 
grammes  of  phosphorus  obtained  from  bones  bought 
at  the  butcher's  by  Pasteur.  These  he  had  calcined, 
submitted  to  the  processes  known  to  chemists,  and 


8  LOUIS  PASTEUR. 

finally  reduced,  after  a  whole  day's  heating,  from  four 
in  the  morning  to  nine  in  the  evening,  to  the  said 
sixty  grammes.  It  was  the  first  time  that  the  long 
manipulations  required  in  the  preparation  of  this 
simple  substance  were  attempted  at  the  Ecole  Nor- 
male. 

Isolated  in  laboratory  or  library,  Pasteur's  only 
thought  was  to  search,  to  learn,  to  question,  and  to 
verify.  As  the  rule  of  the  school  leaves  much  to 
individual  initiative,  he  devoted  himself  to  his  work 
with  a  joyful  heart.  This  daily  liberty  constitutes 
the  charm  and  the  honour  of  the  Ecole  Normale.  Not 
only  does  it  permit  but  it  encourages  individual  effort; 
it  allows  the  student  to  visit  at  his  will  the  library, 
and  to  consult  there  the  scientific  journals  and  reviews.. 
This  free  system  of  education  develops  singularly  the 
spirit  of  research.  There  is  in  it  an  element  of 
superiority  over  the  Ecole  Polytechnique.  Influenced 
by  its  military  origin,  constrained,  moreover,  by  the 
number  of  its  pupils  to  impose  on  all  an  exact  disci- 
pline, and  to  introduce  into  their  exercises  a  strict 
regularity,  the  Ecole  Polytechnique  is,  perhaps,  less 
calculated  than  the  Ecole  Normale  to  awaken  in  the 
minds  of  its  pupils  a  taste  for  speculative  science. 
It  is  certain  that  Pasteur  owed  to  the  freedom  of  work, 
and  to  the  facilities  for  solitary  reading  which  he  there 
enjoyed,  the  first  occasion  for  an  investigation  which 
was  the  starting-point  to  a  veritable  discovery. 


FIEST  DISCOVERIES. 


I. 

Unlike  the  old  professor  of  physics  and  chemistry 
at  Besan9on,  one  of  the  lecturers  in  the  Ecole  Normale 
often  took  pleasure,  not  only  in  answering  Pasteur's 
questions,  but  in  leading  him  on  to  talk  over  scientific 
subjects.  M.  Delafosse,  whose  memory  remains  dear 
to  all  his  pupils,  was  one  of  those  men  who  fail  to  do 
themselves  justice,  or  wrho,  according  to  the  expression 
of  Cardinal  de  Retz,  do  not  fulfil  all  their  merit.  Not 
that  circumstances  have  been  unfavourable  to  them, 
but  that  an  invincible  modesty,  and  a  natural  non- 
chalance which  finds  in  that  modesty  a  shield  against 
latent  self-reproach,  leave  them  in  a  sort  of  twilight 
in  which  they  are  content  to  dwell.  Pupil,  and  after- 
wards fellow  worker,  of  the  celebrated  crystallographer 
Haiiy,  M.  Delafosse  had  devoted  himself  to  questions 
of  molecular  physics.  Pasteur,  who  had  read  with 
enthusiasm  the  works  of  Haiiy,  conversed  incessantly 
with  Delafosse  about  the  arrangements  of  molecules, 
when  an  unexpected  note  from  the  German  chemist 
Mitscherlich,  communicated  to  the  Academy  of 
Sciences,  came  to  trouble  all  his  scientific  beliefs. 
Here  is  the  note : — 

'  The  paratartrate  and  the  tartrate  of  soda  and 
ammonia  have  the  same  chemical  composition,  the 
same  crystalline  form,  the  same  angles,  the  same 


10  LOUIS  PASTEUR. 

specific  weight,  the  same  double  refraction,  and  con- 
sequently the  same  inclination  of  the  optic  axes. 
Dissolved  in  water,  their  refraction  is  the  same.  But 
while  the  dissolved  tartrate  causes  the  plane  of  polar- 
ised light  to  rotate,  the  paratartrate  exerts  no  such 
action.  M.  Biot  has  found  this  to  be  the  case  with  the 
whole  series  of  these  two  kinds  of  salts.  Here  (adds 
Mitscherlich)  the  nature  and  the  number  of  the 
atoms,  their  arrangement,  and  their  distances  apart 
are  the  same  in  the  two  bodies.' 

Imbued  as  he  was  with  the  teachings  of  Haiiy  and 
Delafosse,  and  full  of  the  ideas  of  M.  Dumas  in  mole- 
cular chemistry,  Pasteur  asked  himself  this  question  : 
'  How  can  it  be  admitted  that  the  nature  and  number 
of  the  atoms,  their  arrangement  and  distances  apart, 
in  two  chemical  substances  are  the  same ;  that  the 
crystalline  forms  are  equally  the  same,  without  con- 
cluding that  the  two  substances  are  absolutely  iden- 
tical ?  Is  there  not  a  profound  incompatibility  between 
the  identity  affirmed  by  Mitscherlich  and  the  dis- 
crepancy of  optic  character  manifested  by  the  two 
compounds,  tartaric  and  paratartaric,  which  form  the 
subject  of  his  note  ? ' 

This  difficulty  rested  in  Pasteur's  mind  with  the 
tenacity  of  a  fixed  idea.  Eeceived  as  agrege  of  physical 
science  at  the  end  of  his  third  year  at  the  Ecole,  and 
then  keeping  near  his  master,  M.  Balard,  he  had 
begun  the  study  of  crystals  and  the  determination  of 


FIRST  DISCOVERIES.  11 

their  angles  and  forms,  when  his  nomination  to  the 
professorship  of  physics  in  the  Lycee  of  Tournon 
surprised  and  distressed  him.  M.  Balard  repaired 
immediately  to  the  bureau  of  the  Minister  of  Educa- 
tion, and  spoke  of  his  assistant  in  terms  which  caused 
the  nomination  to  be  cancelled.  Pasteur  remained  in 
the  laboratory  of  the  Ecole  Normale. 

With  a  view  to  mastering  the  science  of  crystal- 
lography, he  took  for  his  guide  the  extensive  work 
of  M.  de  la  Provostaye,  resolving  to  repeat  all  the 
measurements  of  angles  and  all  the  other  determina- 
tions of  this  author  with  a  view  to  a  comparison  of 
their  respective  results.  The  work  of  M.  de  la  Pro- 
vostaye, who  was  distinguished  by  the  exactitude  of 
his  researches,  had  for  its  subject  the  tartaric  and 
paratartaric  acids  and  their  saline  compounds. 

Two  or  three  years  ago,  while  we  wrere  walking  to- 
gether along  a  road  in  the  Jura,  M.  Pasteur,  after 
quoting  textually  the  note  of  Mitscherlich,  described 
to  me  with  enthusiasm  the  pleasure  he  had  experienced 
in  crystallising  tartaric  acid  and  its  salts,  the  crystals 
of  which,  he  said,  rivalled  in  size  and  beauty  the  most 
exquisite  of  crystalline  forms. 

'I  should  have  great  difficulty,'  I  remarked,  'in 
following  you  through  the  labyrinth  of  tartaric  acid, 
tartrates,  and  paratartrates.  However  much  your 
other  studies  have  attracted  me,  those  which  had  for 


12  LOUIS  PASTEUR. 

their  starting-point  the  note  of  Mitscherlich  and  the 
memoir  of  M.  de  la  Provostaye  have  appeared  to  me, 
whenever  I  tried  to  master  them,  difficult  of  access. 
Ah,'  I  added,  '  you  would  have  done  well,  out  of  con- 
sideration for  those  who  love  to  speak  of  your  labours, 
had  you  made  no  discoveries  in  this  field.' 

Pasteur,  with  a  mixture  of  indignation  and  indul- 
gence, replied : — '  Is  it  possible  that  you  have  not 
discerned  the  grand  horizons  that  lie  behind  these 
researches  in  physics  and  molecular  optics  ?  If  I 
have  a  regret,  it  is  that  I  did  not  follow  out  this  path. 
Less  rough  than  it  at  first  sight  appears,  it  would,  I 
am  convinced,  have  led  to  the  most  important  dis- 
coveries. By  a  sudden  turn  it  threw  me  unexpectedly 
upon  the  subject  of  fermentation,  and  fermentation 
led  me  to  the  study  of  diseases ;  but  I  still  continue 
to  lament  that  I  have  never  had  time  to  retrace  my 
steps.' 

Then,  with  a  simplicity  of  exposition  in  which  one 
recognised  the  teacher  who  had  always  endeavoured 
to  place  his  ideas  within  the  range  of  his  hearers,  he 
said — 

'  If  you  picture  to  yourself  all  the  bodies  in  nature 
— mineral,  animal,  or  vegetable,  and  consider  even 
the  objects  formed  by  the  hands  of  man,  you  will  see 
that  they  divide  themselves  into  two  great  categories. 
The  one  has  a  plane  of  symmetry  and  the  other  has 
not.  Take,  for  instance,  a  table,  a  chair,  a  playing 


FIEST   DISCOVERIES.  13 

die,  or  the  human  body ;  we  can  imagine  a  plane 
passing  through  these  objects  which  divides  each  of 
them  into  two  absolutely  similar  halves.  Thus,  a 
plane  passing  through  the  middle  of  the  seat  and  of 
the  back  of  an  arm-chair  would  have,  on  its  right 
and  left,  identical  parts ;  in  like  manner  a  vertical 
plane  passing  through  the  middle  of  the  forehead, 
nose,  mouth,  and  chin  of  an  individual,  would  have 
similar  parts  to  the  right  and  to  the  left.  All  these 
objects,  and  a  multitude  of  similar  ones,  constitute 
our  first  category.  They  have,  as  mathematicians 
express  it,  one  or  several  planes  of  symmetry. 

*  But,  as  regards  the  repetition  of  similar  parts,  it 
is  far  from  being  the  case  that  all  bodies  are  constituted 
in  the  manner  here  described.  Consider,  for  example, 
your  right  hand :  it  is  impossible  to  find  for  it  a  plane 
of  symmetry.  Whatever  be  the  position  of  a  plane 
which  you  imagine  cutting  the  hand,  you  will  never 
find  on  the  right  of  this  plane  exactly  the  same  as 
you  find  on  its  left.  The  same  remark  applies  to 
your  left  hand,  to  your  right  ear  and  to  your  left  ear, 
to  your  right  eye  and  to  your  left  eye ;  to  your  two 
arms,  your  twro  legs,  and  your  two  feet.  The  human 
body,  taken  as  a  whole,  has  a  plane  of  symmetry, 
but  none  of  the  parts  composing  one  or  the  other  of 
its  halves  has  such  a  plane.  The  stalk  of  a  plant 
whose  leaves  are  distributed  spirally  round  its  stem 
has  not  a  plane  of  symmetry,  nor  has  a  spiral  stair- 


14  LOUIS  PASTEUR. 

case  such  a  plane  ;  but  a  straight  one  has.  You  see 
this? 

'  It  would  have  been  truly  extraordinary,  would  it 
not,  if  the  various  kinds  of  minerals,  such  as  sea  salt, 
alum,  the  diamond,  rock  crystal,  and  so  many  others 
which  illustrate  the  great  law  of  crystallisation,  and 
which  clothe  themselves  in  geometric  forms,  should 
not  present  to  us  examples  of  the  two  categories  of 
which  we  have  just  been  speaking  ?  They  do  so  in 
fact.  Thus  a  cube,  which  has  the  form  of  a  player's 
die,  has  a  plane  of  symmetry ;  it  has  indeed  several 
planes.  The  form  of  the  diamond,  which  is  a  regular 
octahedron,  has  also  several  planes  of  symmetry.  It 
is  thus  also  with  the  great  majority  of  the  mineral 
forms  met  with  in  nature  or  in  the  laboratory.  They 
have  generally  one  or  several  planes  of  symmetry. 
There  are,  however,  exceptions.  Eock  crystal,  which 
is  found  in  prisms,  often  of  large  volume,  in  the 
fissures  of  certain  primitive  rocks,  has  no  plane  of 
symmetry.  This  crystal  exhibits  certain  small  facets, 
distributed  in  such  a  manner  that  in  their  totality 
they  might  be  compared  to  a  helix,  or  spiral,  or 
screw,  which  are  all  objects  not  possessing  a  plane  of 
symmetry. 

'Every  object  which  has  a  plane  of  symmetry,  when 
placed  before  a  looking-glass,  has  an  image  which  is 
rigorously  identical  with  the  object  itself.  The  image 
can  be  superposed  upon  the  reality.  Place  a  chair 


FIRST  DISCOVERIES.  15 

before  a  mirror ;  the  image  faithfully  reproduces  the 
chair.  The  mirror  also  reproduces  the  human  body 
considered  as  a  whole.  But  place  before  the  mirror 
your  right  hand  and  you  will  see  a  left  hand.  The 
right  hand  is  not  superposable  on  the  left,  just  as 
the  glove  of  your  right  hand  cannot  be  fitted  to  your 
left,  and  inversely.' 

Then  reverting  to  the  beginnings  of  his  studies  in 
crystallography,  Pasteur  recounted  to  me  briefly  that, 
after  having  gone  through  the  work  of  M.  de  la  Pro- 
vostaye,  he  perceived  that  a  very  interesting  fact  had 
escaped  the  notice  of  this  skilful  physicist.  M.  de  la 
Provostaye  had  failed  to  observe  that  the  crystalline 
forms  of  tartaric  acid  and  of  its  compounds  all  belong 
to  the  group  of  objects  which  have  not  a  plane  of 
symmetry.  Certain  minute  facets  had  escaped  him. 
In  other  words,  Pasteur  discerned  that  the  crystal- 
line form  of  tartaric  acid,  placed  before  a  mirror,  pro- 
duced an  image  which  was  not  superposable  upon  the 
crystal  itself.  The  same  was  found  to  be  true  of 
the  forms  of  all  the  chemical  compounds  of  this  acid. 
On  the  other  hand,  he  imagined  that  the  crystal- 
line form  of  paratartaric  acid,  and  of  all  the  com- 
pounds of  this  acid,  would  be  found  to  form  part 
of  the  group  of  natural  objects  which  have  a  plane  of 
symmetry. 

Pasteur  was  transported  with  joy  by  this  double 
result.  He  saw  in  it  the  possibility  of  reaching  by 


16  LOUIS  PASTEUK. 

experiment  the  explanation  of  the  difficulty  which 
the  note  of  Mitscherlich  had  thrown  down  as  a  kind 
of  challenge  to  science,  when  it  signalised  an  optical 
difference  between  two  chemical  compounds  affirmed 
to  be  otherwise  rigorously  identical.  Pasteur  reasoned 
thus  : — Since  I  find  tartaric  acid  and  all  its  tartratea 
without  a  plane  of  symmetry,  while  its  isomer,  para- 
tartaric  acid,  and  its  compounds  have  such  a  plane,  I 
will  hasten  to  prepare  the  tartrate  and  the  paratartrate 
of  the  note  of  Mitscherlich.  I  will  compare  their 
forms,  and  in  all  probability  the  tartrate  will  be  found 
dissymmetrical — that  is  to  say,  without  a  plane  of 
symmetry — while  the  paratartrate  will  continue  to 
have  such  a  plane.  Henceforward  the  absolute  iden- 
tity stated  by  Mitscherlich  to  exist  between  the  forms 
of  these  two  compounds  will  have  no  existence.  It 
will  be  proved  that  he  has  erred,  and  his  note  will  no 
longer  have  in  it  anything  mysterious.  As  the  optic 
action  proper  to  the  tartrates  spoken  of  in  his  note 
manifests  itself  by  a  deviation  of  the  plane  of  polarisa- 
tion to  the  right,  we  have  here  a  kind  of  dissymmetry 
which  has  nothing  incompatible  with  the  dissymmetry 
of  form.  On  the  contrary,  these  two  dissymmetries 
can  be  referred  to  one  and  the  same  cause.  In  like 
manner,  the  absence  of  dissymmetry  in  the  form  of 
the  paratartrate  will  be  connected  with  the  optical 
neutrality  of  that  compound. 

The  fulfilment  of  Pasteur's  hopes  was  only  partial. 


FIRST  DISCOVERIES.  17 

The  tartrates  of  soda  and  ammonia  presented,  as  did 
all  the  other  tartrates,  the  dissymmetry  manifested  by 
the  absence  of  any  plane  of  symmetry  ;  that  is  to  say, 
the  crystals  of  this  salt  placed  before  a  mirror  pro- 
duced an  image  which  was  not  superposable  upon  the 
crystal.  It  was  like  a  right  hand  having  its  left  for 
an  image.  With  regard  to  the  paratartrates  of  soda 
and  ammonia,  one  circumstance  struck  Pasteur  in  a 
quite  unexpected  manner.  Far  from  establishing  in 
the  crystals  of  this  salt  the  absence  of  all  dissymmetry, 
he  found  that  they  all  manifestly  possessed  it.  But, 
strange  to  say,  certain  crystals  possessed  it  in  one 
sense  and  other  crystals  in  a  sense  opposite.  Some 
of  these  crystals,  when  placed  before  a  mirror,  produced 
the  image  of  the  others,  and  one  of  the  two  kinds  of 
crystals  corresponded  rigorously  in  form  with  the  tar- 
trate  prepared  by  means  of  the  tartaric  acid  of  the 
grape.  Pasteur  continued  his  reasoning  thus: — Since 
there  is  no  difference  between  the  form  of  the  tartrate 
derived  from  the  tartaric  acid  of  the  grape  and  one  of 
the  two  kinds  of  crystals  deposited  at  the  moment  of 
crystallisation  of  the  paratartrate,  the  simple  observa- 
tion of  the  dissymmetry  proper  to  each  will  enable  me 
to  separate,  by  hand,  all  the  crystals  of  the  paratartrate 
which  are  identical  with  those  of  the  tartrate.  By 
ordinary  chemical  processes  I  ought  to  be  able  to  ex- 
tract a  tartaric  acid  identical  with  that  of  the  grape, 
possessing  all  its  physical,  mineralogical,  and  chemical 


18  LOUIS  PASTEUE. 

properties — that  is  to  say,  a  tartaric  acid  possessing, 
like  the  natural  tartaric  acid  of  the  grape,  dissymmetry 
of  form,  and  exerting  an  action  on  polarised  light. 
Per  contra,  I  ought  to  be  able  to  extract  from  the 
second  sort  of  crystals,  associated  with  the  former  in 
the  paratartaric  group,  an  acid  which  will  reproduce 
ordinary  tartaric  acid,  but  possessing  a  dissymmetry 
of  an  inverse  kind  and  exerting  an  action  equally  in- 
verse on  polarised  light. 

With  a  feverish  ardour  Pasteur  hastened  to  make 
this  double  experiment.  Imagine  his  joy  when  he 
saw  his  anticipations  not  only  realised  but  realised 
with  an  exactitude  truly  mathematical.  His  delight 
was  so  great  that  he  quitted  the  laboratory  abruptly. 
Hardly  had  he  gone  out  when  he  met  the  assistant  of 
the  physical  professor.  He  embraced  him,  exclaim- 
ing, '  My  dear  Monsieur  Bertrand,  I  have  just  made  a 
great  discovery  !  I  have  separated  the  double  para- 
tartrate  of  soda  and  ammonia  into  two  salts  of  inverse 
dissymmetry,  and  exerting  an  inverse  action  on  the 
plane  of  polarisation  of  light.  I  am  so  happy  that  a 
nervous  tremulousness  has  taken  possession  of  me, 
which  prevents  me  from  looking  again  through  the 
polariscope.  Let  us  go  to  the  Luxembourg,  and  I  will 
explain  it  all  to  you.' 

These  results  excited  in  a  high  degree  the  attention 
of  the  Academy  of  Sciences,  where  sat,  at  the  time  now 
referred  to,  Arago,  Biot,  Dumas,  De  Senarmont,  and 


FIRST  DISCOVERIES.  19 

Balard.  It  might  be  said  without  exaggeration 
that  the  Academy  was  astounded.  At  the  same 
time  there  were  many  members  who  were  slow  to  be- 
lieve in  this  discovery.  Charged  with  drawing  up  the 
report,  M.  Biot  began  by  requiring  from  Pasteur  the 
verification  of  each  point  which  he  had  announced. 
To  this  verification  M.  Biot  brought  his  habitual  pre- 
cision, which  was  associated  with  a  kind  of  suspicious 
scepticism. 

In  one  of  his  lectures  Pasteur  thus  described  his 
interview  with  M.  Biot : — '  He  made  me  come  to  his 
house,  where  he  put  into  my  handssome  paratartaric 
acid  which  he  had  carefully  studied  himself,  and  found 
perfectly  neutral  as  regards  polarised  light.  It  was 
not  in  the  laboratory  of  the  Ecole  Normale,  it  was  in 
his  own  kitchen,  and  in  his  presence,  that  I  was  to  pre- 
pare this  double  salt  with  soda  and  ammonia  procured 
by  himself.  The  liquor  was  left  slowly  to  evaporate, 
and  at  the  end  of  ten  days,  when  it  had  deposited 
thirty  or  forty  grammes  of  crystals,  he  begged  me  to 
go  over  to  the  College  de  France  to  collect  the  crystals 
and  to  extract  from  them  specimens  of  the  two  kinds, 
which  he  proposed  to  have  placed,  the  one  on  his  right 
hand,  the  other  on  his  left,  desiring  me  to  declare  if  I 
was  ready  to  re-affirm,  that  the  crystals  to  the  right 
would  turn  the  plane  of  polarisation  to  the  right  and 
the  others  to  the  left.  This  declaration  made,  he 
said  that  he  would  charge  himself  with  the  rest  of 


20  LOUIS  PASTEUR. 

the  inquiry.  M.  Biot  then  prepared  the  solutions  in 
well-measured  proportions,  and  at  the  moment  of 
observing  them  in  the  polarising  apparatus  he  invited 
me  again  to  come  into  his  study.  He  placed  first  in 
the  apparatus  the  most  interesting  solution,  that  which 
ought  to  deviate  to  the  left.  Without  even  making  any 
measurements,  he  saw,  by  the  mere  inspection  of  the 
colours  of  the  ordinary  and  extraordinary  images  of  the 
analyser,  that  there  was  a  strong  deviation  to  the  left. 
Visibly  moved,  the  illustrious  old  man  took  my  arm 
and  said,  "My  dear  child,  I  have  loved  science  so  well 
throughout  my  life  that  this  makes  my  heart  beat."  ' 

The  emotion  of  M.  Biot  was  all  the  more  profound 
because  he  had  been  himself  the  first  to  discover  the 
rotation  of  the  plane  of  polarisation  by  chemical  sub- 
stances, and  had,  for  more  than  thirty  years,  affirmed 
that  the  study  of  these  substances  and  of  their  action 
in  regard  to  rotatory  polarisation  was,  perhaps,  the 
surest  means  of  penetrating  into  the  intimate  consti- 
tution of  bodies.  His  counsels  were  received  with 
deference,  but  they  had  never  been  followed  out.  And 
now  there  appeared  before  the  old  man,  already  some- 
what discouraged,  a  youth  of  twenty-five,  who  from  his 
first  investigation  had  proved  himself  a  master,  who 
had  dissipated  the  obscurities  of  the  famous  German 
note,  and  created  a  new  chapter  in  crystallographic 
chemistry.  The  composition  and  nature  of  paratartaric 
acid  had  been  explained,  and  a  new  substance,  the 


FIRST  DISCOVERIES.  21 

left-handed  tartaric  acid,  with  its  truly  surprising 
properties,  had  been  discovered ;  molecular  physics 
and  chemistry  had  been  enriched  with  new  facts  and 
theories  of  great  value. 

The  first  care  of  Pasteur,  after  having  discovered 
the  left-handed  tartaric  acid  and  the  constitution  of 
paratartaric  acid,  was  to  compare  very  carefully  the 
properties  of  the  new  left-handed  acid  with  those  of  the 
right,  endeavouring  to  determine  by  strict  experiment 
the  influence  on  these  properties  of  the  internal 
atomic  arrangements  of  the  two  acids.  Although  we 
are  unable  to  picture  the  exact  figure  of  these  atomic 
groupings,  there  can  be  no  doubt  that  they  are  formed 
of  the  same  elementary  particles,  that  they  are,  more- 
over, dissymmetrical,  and  that,  in  short,  the  dissymme- 
try of  the  one  group  is  the  same  as  that  of  the  other, 
but  in  an  inverse  sense.  If,  for  example,  the  arrange- 
ment of  the  atoms  of  the  right-handed  tartaric  acid 
present  the  exterior  appearance  of  an  irregular  pyra- 
mid, the  arrangement  of  the  atoms  of  the  left-handed 
tartaric  acid  ought,  of  necessity,  to  present  the  form 
of  a  pyramid  irregular  in  the  inverse  sense. 

II. 

Nominated  assistant  professor  of  chemistry  at 
Strasburg,  Pasteur  followed  up  with  enthusiasm  these 
curious  studies.  To  interrupt  them  for  an  instant  it 


22  LOUIS  PASTEUE. 

required  nothing  less  than  his  engagement  with 
Mademoiselle  Marie  Laurent,  daughter  of  the  Eector 
of  the  Academy.  It  is  even  asserted  that  on  the  very 
morning  of  his  marriage  it  was  necessary  to  go  to  his 
laboratory  and  remind  him  of  the  event  that  was  to 
take  place  on  that  day.  But  if  Pasteur  was  thus  guilty 
of  an  absent-mindedness  worthy  of  La  Fontaine,  he 
proved  as  a  husband  so  different  from  La  Fontaine 
that  Madame  Pasteur,  when  reminded  of  this  lapse 
of  memory,  receives  the  reminder  with  an  indulgent 
smile. 

But  to  return  to  the  laboratory  :  Under  the  same 
conditions  of  weight,  temperature,  and  quantity  of 
solvent,  Pasteur  placed  successively,  in  presence  of  the 
two  acids,  all  the  substances  capable  of  combining 
with  them.  In  this  way  he  obtained  right-handed 
and  left-handed  tartrates  of  potash,  of  soda,  of  am- 
monia, of  lime,  and  of  all  the  oxides  properly  so  called. 
He  applied  himself  to  the  compounds — and  they  are 
numerous — which  deposit  themselves  in  liquids  under 
well-determined  crystalline  forms.  Without  entering 
into  the  details  of  these  long  and  patient  studies,  it 
may  be  stated  generally  that  Pasteur  proved  that 
whatever  could  be  done  with  one  of  the  tartaric  acids 
could  be  repeated  rigorously,  under  similar  conditions, 
with  the  other,  the  resultant  products  manifesting 
constantly  the  same  properties,  with  the  single  differ- 
ence already  exhibited  by  the  two  acids — that  in  the 


FIEST  DISCOVERIES.  23 

one  case  the  deviation  of  the  plane  of  polarisation  was 
to  the  right,  while  in  the  other  it  was  to  the  left.  With 
regard  to  all  their  other  properties,  both  chemical  and 
physical,  the  identity  was  absolute.  Solubility,  simple 
refraction  by  solutions,  double  refraction  by  crystals, 
the  action  of  heat  in  producing  decomposition,  &c., 
the  similitude  extended  to  the  most  perfect  identity. 

The  Academy  of  Sciences,  which  shows  by  the 
rarity  of  its  reports  the  importance  which  it  attaches 
to  them,  gave  for  the  second  time  an  account  of  these 
new  researches.  M.  Biot  was  again  the  reporter.  It 
was  with  a  sort  of  coquetry  that  Pasteur  brought  from 
Strasburg  perfectly  labelled  specimens  of  the  magnifi- 
cent crystallisations  of  the  double  series  of  right- 
handed  and  left-handed  tartrates.  By  means  of 
models  he  was  able  to  render  the  forms  of  these 
crystals  visible  at  a  distance. 

M.  Biot  undertook  to  bring  the  subject  before  the 
Academy.  On  the  morning  of  the  day  when  he  was 
to  read  his  report  he  spent  several  hours  in  conversa- 
tion with  Pasteur.  M.  Biot  became  so  excited  during 
the  discussion  that  Madame  Biot,  with  the  solici- 
tude peculiar  to  the  wives  of  Academicians,  requested 
Pasteur  to  change  the  subject  of  conversation. 

The  members  of  the  Academy  shared  the  enthu- 
siasm of  M.  Biot.  Arago  moved  that  the  report 
be  inserted  in  the  collected  memoires  of  the  Academy. 
This  was  an  exceptional  honour.  Arrived  for  the  most 


24  LOUIS  PASTEUK. 

part  at  the  end  of  their  own  careers,  these  learned  men 
observed  with  pleasure  the  incipient  ray  which  had 
not  yet  become  a  glory  but  which  was  the  precursor 
thereof. 

'My  young  friend,'  said  M.  Biot  to  Pasteur,  when 
presenting  him  to  Mitscherlich  somewhere  about  that 
time,  '  you  may  boast  of  having  done  something  great, 
in  having  discovered  what  had  escaped  such  a  man  as 
this.' 

'  I  had  studied,'  replied  Mitscherlich,  not  without 
a  shade  of  regret,  addressing  himself  to  Pasteur,  '  I 
had  studied  with  so  much  care  and  perseverance,  in 
their  smallest  details,  the  two  salts  which  formed  the 
subject  of  my  note  to  the  Academy,  that,  if  you  have 
established  what  I  was  unable  to  discover,  you  must 
have  been  guided  to  your  result  by  a  preconceived 
idea.' 

Mitscherlich  was  right,  and  this  preconceived  idea 
might  have  been  formulised  thus :  A  dissymmetry  in 
the  internal  molecular  arrangement  of  a  chemical  sub- 
stance ought  to  manifest  itself  in  all  its  external  pro- 
perties which  are  themselves  capable  of  dissymmetry. 

If  this  theoretic  conception  was  correct,  Pasteur 
might  expect  to  find  that  all  the  substances  in  which 
M.  Biot  had  observed  the  power  of  rotating  the  plane  of 
polarisation  would  possess  the  crystalline  dissymmetry 


FIEST  DISCOVEKIES.  25 

revealed  by  the  absence  of  superposability.  The  result 
was  in  great  part  conformable  to  those  previsions. 
The  substances  which  acted  upon  polarised  light,  as 
liquids  or  solutions,  were  generally  found  by  Pasteur 
to  produce  dissymmetric  crystals.  Some  of  them,  how- 
ever, notwithstanding  their  power  of  crystallisation, 
exhibited,  when  crystallised,  no  dissymmetric  face. 
This  difficulty  did  not  deter  Pasteur.  It  gave  him,  on 
the  contrary,  the  opportunity  of  showing  that  when  a 
theory  had  in  so  many  cases  proved  itself  correct,  an 
apparent  objection  must  not  be  assumed  insuperable 
without  first  sounding  it  to  the  bottom.  May  it  not 
be,  he  reasoned,  that  the  absence  of  dissymmetry  in 
substances  which  have  the  molecular  rotatory  power 
is  not  an  accident ;  and  may  it  not  be  possible,  by 
changing  the  conditions  of  the  crystallisation,  to  make 
the  dissymmetry  appear  ? 

Then,  in  order  to  modify  the  crystalline  forms  of 
substances  which  did  not  show  themselves  to  be  spon- 
taneously dissymmetrical,  Pasteur  employed  a  method 
which  had  been  often  tried  before,  though  its  principles 
could  not  be  explained  or  its  effects  foreseen.  In 
imitation  of  Eome  de  Lisle,  Leblanc,  and  Beudant,  he 
varied  the  nature  of  his  solvents ;  he  introduced  into 
the  solution,  sometimes  an  excess  of  acid  or  of  base, 
sometimes  foreign  matters  incapable  of  acting  chemi- 
cally upon  those  which  wrere  to  be  modified  ;  he  even 
employed  sometimes  impure  mother  liquids.  On  each 


26  LOUIS  PASTEUE. 

occasion  new  facets  were  thus  produced,  and  these 
new  facets  showed  the  kind  of  dissymmetry  which  the 
optical  character  demanded.  Although  he  had  to 
limit  his  researches  to  those  substances  which,  by 
their  ready  crystallisation  and  the  beauty  of  their 
forms,  lent  themselves  best  to  this  class  of  proofs,  the 
results  were  so  far  in  accord  with  the  previsions  of 
theory,  that  no  reasonable  doubt  could  exist  as  to  the 
necessary  correlation  between  dissymmetry  and  the 
power  to  deviate  polarised  light. 

By  these  researches  Pasteur  was  led  to  a  conclu- 
sion, which  is  worthy  of  the  most  serious  considera- 
tion, regarding  the  difference  which  exists  between 
mineral  species  and  artificial  products  on  the  one 
side,  and  the  organic  products  which  can  be  ex- 
tracted from  vegetables  or  animals  on  the  other.  All 
mineral  or  artificial  products — for  brevity  let  us  say 
all  the  products  of  inorganic  nature — have  a  super- 
posable  image,  and  are  therefore  not  dissymmetrical, 
while  vegetable  and  animal  products — in  other  words, 
products  formed  under  the  influence  of  life — have  an 
image  not  superposable ;  that  is  to  say,  they  are 
atomically  dissymmetrical,  this  dissymmetry  express- 
ing itself  externally  in  the  power  of  turning  the 
plane  of  polarisation.  If  any  exceptions  exist  they 
are  more  apparent  than  real.  Pasteur  himself  pointed 
out  some  of  them,  while  demonstrating  at  the  same 


FIRST  DISCOVERIES.  27 

time  that  it  is  easy  to  explain  why  all  trace  of  dis- 
symmetry disappears  when  substances  which,  like  rock 
crystal,  have  an  external  dissymmetry  are  subjected 
to  the  process  of  solution. 

An  apparent  contradiction  to  this  law  of  demarca- 
tion between  artificial  products  and  those  of  animal 
and  vegetable  life  is  presented  by  the  existence  in 
living  creatures  of  substances  like  oxalic  acid,  formic 
acid,  urea,  uric  acid,  creatine,  &c.  None  of  these  pro- 
ducts exert  an  action  on  polarised  light  or  show  any 
dissymmetry  in  the  form  of  their  crystals.  But  it  is 
necessary  to  observe  that  these  products  are  the  result 
of  secondary  actions.  Their  formation  is  evidently 
governed  by  the  laws  which  determine  the  constitu- 
tion of  the  artificial  products  of  our  laboratories,  or  of 
the  mineral  kingdom  properly  so  called.  In  living 
beings  they  are  the  products  of  excretion  rather  than 
substances  essential  to  vegetable  or  animal  life. 
When,  on  the  other  hand,  we  consider  the  most 
primordial  substances  of  vegetables  and  animals — 
those  whereof  it  may  be  justly  said  that  they  are  born 
under  the  directive  influence  of  becoming  life,  such  as 
cellulose,  fecula,  albumen,  fibrine,  &c.— they  are  found 
to  possess  the  power  of  acting  on  polarised  light,  a 
characteristic  necessary  and  sufficient  to  establish 
their  internal  dissymmetry,  even  when,  through  the 
absence  of  crystallising  power,  they  fail  to  manifest 
this  dissymmetry  outwardly. 


28  LOUIS  PASTEUK. 

It  is,  therefore,  true  to  say  that  the  products  of 
inorgajiia^Dature,  whether  mineral  or  artificial,  have 
never  yet  presented  molecular  dissymmetry.  It  may 
also  be  affirmed  that  the  substances  which  exert  the 
greatest  influence  in  vital  manifestations,  which  are 
present  and  active  in  the  seed  and  in  the  egg  at  the 
moment  of  the  marvellous  start  of  animal  and  vege- 
table life,  all  present  molecular  dissymmetry. 

Would  it  be  possible  to  indicate  a  more  profound 
distinction  between  the  respective  products  of  living 
and  of  mineral  nature,  than  the  existence  of  this 
dissymmetry  on  the  part  of  the  one  and  its  absence 
on  the  part  of  the  other  ?  Is  it  not  strange  that  not 
one  of  these  thousands  and  thousands  of  artificial  pro- 
ducts of  the  laboratory,  the  number  of  which  is  each 
day  augmented,  should  manifest  either  the  power 
of  turning  the  plane  of  polarisation  or  non-super- 
posable  dissymmetry?  No  doubt  natural  dissym- 
metric substances — gum,  sugar,  tartaric  and  malic 
acids,  quinine,  strychnine,  essence  of  turpentine, 
&c. — may  be  employed  in  forming  new  compounds 
which  remain  dissymmetric,  though  they  are  artifi- 
cially prepared ;  but  it  is  evident  that  all  these  new 
products  do  but  inherit  the  original  dissymmetry  of 
the  substances  from  which  they  are  derived.  When 
chemical  action  becomes  more  profound,  all  dissym- 
metry disappears,  and  is  never  seen  to  reappear  in  the 
successive  ulterior  products. 


FIRST  DISCOVERIES.  29 

What  can  be  the  causes  of  so  great  a  difference  ? 
M.  Pasteur  has  often  expressed  to  me  the  conviction 
that  it  must  be  attributed  to  the  circumstance  that 
the  molecular  forces  which  operate  in  the  mineral 
kingdom,  and  which  are  brought  into  play  every  day  in 
our  laboratories,  are  forces  of  the  symmetrical  order  ; 
while  the  forces  which  are  present  and  active  at  the 
moment  when  the  grain  sprouts,  when  the  egg  develops, 
and  when,  under  the  influence  of  the  sun,  the  green 
matter  of  the  leaves  decomposes  the  carbonic  acid 
of  the  air  and  utilises  in  divers  ways  the  carbon  of 
this  acid,  the  hydrogen  of  the  water,  and  the  oxygen 
of  these  two  products — are  of  the  dissymmetric  order, 
probably  depending  on  some  of  the  grand,  dissym- 
metric, cosmic  phenomena  of  our  universe.  While 
expounding  this  opinion  before  the  Academy  of 
Sciences,  Pasteur,  on  one  occasion,  expressed  himself 
thus  : — 

'  The  universe  is  a  dissymmetric  whole.  I  am 
inclined  to  think  that  life,  as  manifested  to  us,  must 
be  a  function  of  the  dissymmetry  of  the  universe  or 
of  the  consequences  that  follow  in  its  train.  The 
universe  is  dissymmetrical;  for,  placing  before  a 
mirror  the  group  of  bodies  which  compose  the  solar 
system,  with  their  proper  movements,  we  obtain  in 
the  mirror  an  image  not  superposable  on  the  reality. 
Even  the  motion  of  solar  light  is  dissymmetrical.  A 
luminous  ray  never  strikes  in  a  straight  line,  and 


Q  t-*— ^    ro^ 

-3Wvvx^A-j5vMH^ -. 


30  LOUIS  PASTEUR. 

at  rest,  the  leaf  wherein  organic  matter  is  created 
by  vegetable  life.  Terrestrial  magnetism,  the  oppo- 
sition which  exists  between  the  north  and  south 
poles  of  a  magnet,  the  opposition  presented  to  us  by 
positive  and  negative  electricity,  are  all  the  resultants 
of  dissymmetric  actions  and  motions.' 

At  the  moment  when  Pasteur,  entering  upon  the 
labours  which  form  the  principal  subject  of  this  book, 
abandoned  the  study  of  molecular  physics  and 
chemistry  which  had  previously  occupied  him,  all 
his  thoughts  were  directed  to  the  search  of  means 
suited  to  render  evident  the  influence  of  these  causes 
and  these  phenomena.  At  Strasburg  he  had  procured 
powerful  magnets  with  the  view  of  comparing  the 
actions  of  their  poles,  and,  if  possible,  of  introducing 
by  their  aid,  among  the  forms  of  crystals,  a  mani- 
festation of  dissymmetry.  At  Lille,  where  he  was 
nominated  Dean  of  the  Faculty  of  Sciences  in  1854, 
he  had  contrived  a  piece  of  clockwrork  intended  to 
keep  a  plant  in  continual  rotary  motion,  first  in  one 
direction  and  then  in  the  other.  '  All  this  was  gross,' 
he  said  to  me  one  day ;  '  but,  further  than  this,  I  had 
proposed,  with  the  view  of  influencing  the  vegetation 
of  certain  plants,  to  invert,  by  means  of  a  heliostat 
and  a  reflecting  mirror,  the  motion  of  the  solar  rays 
which  should  strike  them  from  the  birth  of  their 
earliest  shoots,  and  in  this  direction  there  was  more 


FIRST  DISCOVEEIES.  31 

to  be  hoped  for.'  He  never  spoke  of  these  attempts, 
because  he  had  not  had  the  time  to  follow  them  to 
the  issues  of  which  he  dreamed ;  but  to  this  day 
he  remains  persuaded  that  the  barrier  which  exists 
between  the  mineral  and  organic  kingdoms — and 
which  is  revealed  to  our  eyes  by  the  impossibility  of 
producing,  in  the  reactions  of  the  laboratory,  dissym- 
metric organic  substances — can  never  be  crossed  until 
we  have  succeeded  in  introducing  among  these  re- 
actions influences  of  the  dissymmetric  order.  Accord- 
ing to  Pasteur,  success  in  this  direction  would  give 
access  to  a  new  world  of  substances,  and  probably  also 
of  organic  transformations.  As  we  have  succeeded 
in  finding  the  inverse  of  right-handed  tartaric  acid, 
we  may  hope  to  obtain  some  day  all  the  immediate 
principles  inverse  to  those  now  known  to  us.  Who 
could  say  what  vegetable  and  animal  species  would 
become  if  it  were  possible  to  replace,  hi  the  living 
cells,  cellulose,  albumen,  and  their  congeners,  by  their 
isomers  with  an  inverse  action  ?  Certainly  the  thing 
is  not  easy,  and  Pasteur  would  be  the  last  person  to 
deceive  himself  as  to  the  difficulty  of  the  problem.  His 
latest  thought  on  the  matter  is  this : — When  the 
attempt  is  made  to  introduce  into  living  species  pri- 
mordial substances,  inverse  to  those  now  existing,  the 
great  difficulty  will  be  to  master  the  tendency  (devenir]) 

1  [M.  Pasteur  appears  to  use  the  word  devenir  as  a  substantive 
in  a  sense  equivalent  to  the  German  Werdende.] 

4 


32  LOUIS  PASTEUR. 

proper  to  the  species,  a  tendency  which  is  potential 
in  the  germ  of  each  of  them.  In  this  germ,  it  is 
to  he  feared,  the  dissymmetry  of  the  dissymmetric 
primordial  substances  which  it  embraces  will  always 
manifest  itself.  Ah  !  if  spontaneous  generation  were 
possible ;  if  we  could  form  from  mineral  matter  a 
living  cell,  how  much  more  accessible  would  the 
problem  become  !  However  this  may  be,  we  must 
seek,  by  all  possible  means,  to  produce  molecular 
dissymmetry  by  the  application  of  forces  which  have 
a  dissymmetric  action.  '  We  must,'  said  Pasteur  to 
me  on  the  day  when,  starting  from  the  note  of 
Mitscherlich,  he  passed  all  these  things  in  review, 
'  we  must  invoke  the  action  of  solenoid  or  helix.  En- 
tangled at  present  in  labours  more  than  sufficient  to 
absorb  whatever  of  ardour  and  of  force  still  remains 
to  me,  I  have  no  longer  time  to  occupy  myself  with 
these  questions.'  But  what  great  things  are  to  be 
done  in  following  out  this  order  of  ideas,  and  what  a 
route  will  be  opened  to  young  men  possessed  of  that 
genius  of  invention  which  is  evoked  so  often  by  per- 
sistent work  ! 

This  complete  opposition  between  artificial  mineral 
products  and  vegetable  and  animal  ones  was  to  Pasteur 
a  truth  so  well  established  that  he  found  frequent 
opportunity  of  affirming  it  under  decisive  circum- 
stances. One  day,  a  very  skilful  chemist,  M.  Dessaignes, 


FIRST  DISCOVERIES.  33 

who  later  on  became  one  of  the  correspondents  of  the 
Academy  of  Sciences,  announced  that  he  had  trans- 
formed fumaric  and  malic  acids  into  aspartic  acid. 
Pasteur,  who  some  time  previously  had  had  occasion 
to  study  these  same  acids,  had  proved  that  the  two 
first  had  no  molecular  dissymmetry — that  is  to  say, 
they  exercised  no  optic  action.  In  the  state  of  so- 
lution they  did  not  turn  the  plane  of  polarised  light. 
Aspartic  acid,  on  the  contrary,  had  presented  to  him 
molecular  dissymmetry,  like  asparagine  itself.  If  the 
observation  of  M.  Dessaignes  were  true,  then  bodies 
which  were  inert  in  regard  to  polarised  light,  and  con- 
sequently non-dissymmetric,  could  be  transformed  in 
the  laboratory  into  active  dissymmetric  bodies.  The 
line  of  demarcation  so  well  established  would  be  broken. 
Pasteur,  whose  experience  regarding  the  note  of 
Mitscherlich  had  shown  him  how  even  the  most  con- 
scientious observers  may  fail  to  seize  upon  fugitive 
appearances,  when  unprompted  to  seek  them  by  a 
preconceived  idea,  doubted  at  once  the  accuracy  of  the 
facts  cited  by  M.  Dessaignes.  From  Strasburg  he 
started  for  Vendome,  where  M.  Dessaignes  at  that  time 
resided.  M.  Dessaignes  immediately  gave  Pasteur  a 
small  quantity  of  the  aspartic  acid  which  he  had  pre- 
pared by  means  of  fumaric  and  malic  acids.  Eeturn- 
ing  to  his  laboratory,  Pasteur  immediately  recognised 
that,  despite  the  very  close  resemblance  of  the  new  acid 
of  M.  Dessaignes  to  that  derived  from  asparagine, 


34  LOUIS   PASTEUK. 

the  former  differed  from  the  latter  by  the  complete 
absence  in  its  case  of  molecular  dissymmetry. 

With  regard  to  other  facts  of  the  same  kind,  an- 
nounced not  only  in  France,  but  in  Italy,  and  in 
England — chiefly  the  pretended  formation  of  grape 
tartaric  acid  from  succinic  acid,  artificial  and  inert, 
by  Perkin  and  Duppa — Pasteur  testified  with  absolute 
certainty  of  judgment  to  the  existence  of  phenomenal 
peculiarities  proper  to  these  substances,  which  he  had 
never  seen,  and  which  had,  on  the  other  hand,  been 
the  object  of  careful  study  by  observers  of  great  talent. 

After  these  verifications  and  deductions  from 
theoretic  views,  Pasteur  discovered  a  surprising  con- 
nection between  the  prior  researches  of  chemistry  and 
crystallographic  physics  and  the  new  and  entirely  un- 
expected results  of  physiological  chemistry.  This 
connection,  like  the  thread  of  Ariadne,  conducted  him 
to  his  recent  great  discoveries  in  medical  biology. 
M.  Chevreul  was  right  when,  some  years  ago,  at  the 
Academy  of  Sciences,  he  expressed  himself  thus  :— 

'  It  is  by  first  examining  in  their  chronological  order 
the  researches  of  M.  Pasteur,  and  then  considering 
them  as  a  whole,  that  we  are  enabled  to  appreciate 
the  rigour  of  judgment  of  that  learned  man  in  form- 
ing his  conclusions,  and  the  perspicacity  of  a  mind 
which,  strong  in  the  truths  which  it  has  already  dis- 
covered, is  carried  forward  to  the  establishment  of  new 
ones.' 


FIRST  DISCOVERIES  35 


III. 

Pasteur  had  thus  established  that  bodies  endowed 
with  internal  dissymmetry  carried  this  property,  in 
varying  degrees,  into  their  compounds  or  their  deriva- 
tives. When  two  of  these  bodies  whose  nature  has 
been  revealed  by  the  discovery  of  right-handed  and 
left-handed  tartaric  acid,  where  all  is  chemically  iden- 
tical— and  which  are  only  to  be  distinguished  from 
each  other  by  their  inverse  crystallographic  form,  and 
by  their  action  on  polarised  light — enter  into  combina- 
tion with  a  substance  which  is  optically  and  crystallo- 
graphically  inert,  the  chemical  identity  ought,  under 
these  new  conditions,  to  be  preserved.  Everything 
remains  optically  and  crystallographically  comparable. 
The  inert  element  adds  nothing  to,  and  takes  away 
nothing  from,  the  dissymmetric  faculties  of  the  active 
one. 

To  these  curious  studies  Pasteur  soon  added  a  new 
chapter.  He  reasoned  thus : — If  into  these  compounds 
I  introduce  a  substance  possessing  in  itself  the  specific 
properties  of  dissymmetry,  it  is  evident  that  this  sub- 
stance, while  entering  into  these  combinations,  must 
preserve  its  own  properties.  The  active  substance 
would,  from  the  moment  of  its  combination,  add  some- 
thing to  the  properties  of  the  molecular  group  which 
acts  like  itself,  and  subtract  something  from  the 


36  LOUIS  PASTEUR. 

properties  of  the  group  which  acts  in  the  opposite 
manner.  The  resultant  effect  of  these  actions,  some- 
times concordant,  sometimes  antagonistic,  would  cease 
to  be  alike  in  absolute  quantity.  And  if  this  be  the 
necessary  condition  of  similitude  as  to  molecular 
arrangement,  this  similitude  would  cease  to  exist,  and 
with  its  disappearance  would  appear  all  the  differences 
of  chemical  and  physical  properties  which  constitute 
its  outward  manifestations. 

The  facts  were  found  to  harmonise  with  these 
logical  deductions.  After  having  made  dissymmetry 
intervene  as  a  modifier  of  chemical  affinity,  he  had  a 
strange  and  manifest  proof  of  the  influence  of  dis- 
symmetry in  the  phenomena  of  life. 

It  had  been  long  known,  through  the  observations 
of  a  manufacturer  of  chemical  products  in  Germany, 
that  the  impure  tartrate  of  lime  of  commerce,  if  con- 
taminated with  organic  matters  and  permitted  to 
remain  under  water  in  summer,  would  ferment  and 
yield  various  products.  Pasteur  caused  the  ordinary 
right-handed  tartrate  of  ammonia  to  ferment  in  the 
following  manner  : — He  took  some  very  pure  crystalline 
salt  and  dissolved  it,  adding  at  the  same  time  to  the 
liquid  some  albuminoid  matter,  about  one  gramme  to 
100  grammes  of  the  tartrate.  The  liquid  placed  in 
a  warm  chamber  fermented.  During  the  process  of 
fermentation  the  liquid  mass,  previously  limpid,  be- 
came gradually  turbid,  in  consequence  of  the  appear- 


FIRST  DISCOVERIES.  37 

ance  of  a  small  organism  which  played  the  part  of 
ferment.  Pasteur  applied  this  mode  of  fermentation 
to  the  paratartrate  of  ammonia.  He  saw  that  this 
salt  also  fermented,  depositing  the  same  organism. 
All  appeared  as  if  the  course  of  things  was  the  same 
as  in  the  case  of  the  right-handed  tartrate.  But 
Pasteur,  having  had  the  idea  of  following  the  course 
of  the  operation  with  the  aid  of  the  polariscope,  soon 
detected  a  profound  difference  between  the  two  fer- 
mentations. In  the  case  of  the  paratartrate,  the 
liquid,  at  first  inert,  gradually  assumed  a  sensible 
power  of  deviation  to  the  left,  which  augmented  by 
degrees  and  attained  a  maximum.  The  fermentation 
was  then  suspended ;  there  was  no  longer  any  of  the 
right-handed  acid  in  the  liquid,  which,  when  evaporated 
and  mixed  with  its  own  volume  of  alcohol,  immediately 
furnished  a  beautiful  crystallisation  of  left-handed 
tartrate  of  ammonia. 

From  that  moment  a  great  new  fact  was  esta- 
blished— namely,  that  the  molecular  dissymmetry 
proper  to  organic  matters  intervened  in  a  phenomenon 
of  the  physiological  order,  and  did  so  as  a  modifier 
of  chemical  affinity.  The  kind  of  dissymmetry  proper 
to  the  molecular  arrangement  of  the  left-handed 
tartaric  acid  was,  no  doubt,  the  sole  cause  of  the  dif- 
ference between  this  acid  and  the  right-handed  acid, 
in  regard  to  the  fermentation  produced  by  a  micro- 
scopic fungus.  We  shall  see  later  on  that  organised  fer- 


38  LOUIS  PASTEUR. 

ments  are  almost  always  microscopic  vegetables,  which 
embrace  in  their  constitution  cellulose,  albumen,  &c., 
identical  with  these  same  substances  taken  from  the 
higher  class  of  vegetables  and  equally  dissymmetric. 
We  can  thus  understand,  that  for  the  nutrition  of  the 
ferment  and  the  formation  of  its  principles  the 
chemical  changes  are  more  easy  with  one  of  the  two 
tartaric  acids  than  with  the  other. 

The  opposition  of  the  properties  of  the  two  tartaric 
acids,  right  and  left,  at  the  moment  when  the  condi- 
tions of  life  and  nutrition  of  an  organised  being  inter- 
vened, showed  themselves  still  more  strikingly  in  a 
very  curious  experiment  made  by  Pasteur.  He  was  the 
first  to  prove  that  mildew  could  live  and  multiply  on 
a  purely  mineral  soil,  composed,  for  example,  of  the 
phosphates  of  potash,  of  magnesia,  and  an  ammoniacal 
salt  of  an  organic  acid.  For  such  a  development  of  vege- 
table life  he  employed  the  seed  of  penicillium  glaucum, 
which  is  to  be  found  everywhere  as  common  mould, 
and  to  which  he  offered,  as  its  only  carbon  aliment, 
paratartaric  acid.  At  the  end  of  a  little  time  the  left- 
handed  tartaric  acid  appeared.  Now  this  left-handed 
acid  could  only  show  itself  on  the  condition  that  a 
rigorously  equal  quantity  of  the  right-handed  acid  had 
been  decomposed.  The  carbon  of  the  tartaric  acid 
evidently  supplied  to  the  little  plant  the  carbon  that 
was  necessary  for  the  formation  of  its  constituents  and 
all  their  organic  accessories.  If  the  microscopic  seed 


FIRST  DISCOVERIES.  39 

of  penicillium  sown  upon  this  soil  was  not  formed  of 
dissymmetric  elements,  as  is  the  case  with  all  other 
vegetable  substances,  its  development,  its  life,  its 
fructification  would  accommodate  themselves  equally 
well  with  the  left-handed  tartaric  acid  as  with  the 
right.  The  fact  that  the  left-handed  tartaric  acid  is 
less  assimilable  than  its  opposite^is  due  solely  and 
evidently  to  the  dissymmetry^  of  one  or  other  of  the 
primordial  substances  of  the  little  plant. 

Thus  for  the  first  time  was  introduced  into 
physiological  studies  and  considerations  the  fact  of 
the  influence  of  the  molecular  dissymmetry  of  natural 
organic  products.  ....*  - 

Pasteur  always  speaks  with  enthusiasm  of  the 
grand  future  reserved  for  researches  which  have  this 
influence  for  their  object ;  for  molecular  dissymmetry 
is  the  only  sharp  line  of  demarcation  which  exists  be- 
tween the  chemistry  of  inorganic  and  that  of  organic 
nature. 


40  LOUIS  PASTEUR. 


FERMENTATION. 

ARRIVED  at  this  unexpected  turn  in  the  road  which 
he  had  hitherto  pursued,  Pasteur  paused  for  an  in- 
stant. Should  he  commit  himself  to  the  course  which 
abruptly  opened  before  him  ?  His  scientific  instincts 
urged  him  to  do  so,  but  the  prudence  and  reserve 
which  show  themselves  to  be  the  basis  of  his  character, 
whenever  he  finds  himself  called  upon  to  make  a 
choice  of  which  the  necessiiy  is  not  absolutely  demon- 
strated, held  him  back.  Was  it  not  wiser  to  continue 
in  the  domain  of  molecular  physics  and  chemistry  ? 
M.  Biot  counselled  his  doing  so ;  the  route  had  been 
made  plain,  success  awaited  him  at  each  step,  but  an 
incident  connected  with  the  University  triumphed 
over  his  hesitations. 

He  had  just  been  nominated,  at  thirty-two  years 
of  age,  Dean  of  the  Faculte  des  Sciences  at  Lille.  One 
of  the  principal  industries  of  the  Departement  du  Nord 
is  the  fabrication  of  alcohol  from  beetroot  and  from 
corn.  Pasteur  resolved  to  devote  a  portion  of  his 
lectures  to  the  study  of  fermentation.  He  felt  that  if 


FERMENTATION.  41 

he  could  make  himself  directly  useful  to  his  hearers  he 
would  thereby  excite  general  sympathy  with,  and  direct 
attention  to  the  new  Faculte.  The  young  man  congra- 
tulated himself  on  this  idea,  and  the  man  of  science 
rejoiced  in  it  still  more.  He  was  filled  by  the  reflec- 
tions suggested  to  him  by  the  strangeness  of  the 
phenomena  which  he  had  just  encountered  in  regard 
to  the  molecular  dissymmetry  of  the  two  tartaric  acids, 
in  connection  with  the  life  of  a  microscopic  organism. 
He  saw  new  light  thrown  upon  the  obscure  problem 
of  fermentation.  The  part  so  active  performed  by 
an  infinitely  small  organism  could  not,  he  thought, 
be  an  isolated  fact.  Behind  this  phenomenon  must 
lie  some  great  general  law. 


All  that  has  lived  must  die,  and  all  that  is  dead 
must  be  disintegrated,  dissolved  or  gasified  ;  the  ele- 
ments which  are  the  substratum  of  life  must  enter 
into  new  cycles  of  life.  If  things  were  otherwise,  the 
matter  of  organised  beings  would  encumber  the  surface 
of  the  earth,  and  the  law  of  the  perpetuity  of  life  would 
be  compromised  by  the  gradual  exhaustion  of  its 
materials.  One  grand  phenomenon  presides  over  this 
vast  work,  the  phenomenon  of  fermentation.  But 
this  is  only  a  word,  and  it  suggests  to  the  mind  simply 
the  internal  movements  which  all  organised  matter 
manifests  spontaneously  after  death,  without  the  in- 


42  LOUIS  PASTEUR. 

tervention  of  the  hand  of  man.  What  is,  then,  the 
cause  of  the  processes  of  fermentation,  of  putrefaction, 
and  of  slow  combustion  ?  How  is  the  disappearance 
of  the  dead  body  or  of  the  fallen  plant  to  be  accounted 
for  ?  What  is  the  explanation  of  the  foaming  of  the 
must  in  the  vintage  cask  ?  of  dough,  which,  abandoned 
to  itself,  rises  and  becomes  sour  ?  of  milk,  which 
curdles  ?  of  blood,  which  putrefies  ?  of  the  heap  of  straw, 
which  becomes  manure?  of  dead  leaves  and  plants 
embedded  in  the  earth,  which  transform  themselves 
into  soil  ? 

Many  different  attempts  were  made  to  account  for 
this  mystery  before  science  was  in  a  condition  to  ap- 
proach it.  In  our  age,  and  at  the  time  when  Pasteur 
was  led  to  the  study  of  the  question,  one  theory  held 
almost  undisputed  sway.  It  was  a  very  ancient  theory, 
to  which  Liebig,  in  reviving  it,  had  given  the  weight 
of  his  name.  '  The  ferments,'  said  Liebig,  '  are  all 
nitrogenous  substances — albumen,  fibrine,  caseine ;  or 
the  liquids  which  embrace  them,  milk,  blood,  urine — 
in  a  state  of  alteration  which  they  undergo  in  con- 
tact with  the  air.' 

The  oxygen  of  the  air  was,  according  to  this  system, 
the  first  cause  of  the  molecular  breaking  up  of  the 
nitrogenous  substances.  The  molecular  motions  are 
gradually  communicated  from  particle  to  particle  in 
the  interior  of  the  fermentable  matter,  which  is  thus 
resolved  into  new  products. 


FEKMENTATION.  43 

These  theoretic  ideas  regarding  the  part  played  in 
fermentation  by  the  oxygen  of  the  air  were  based  upon 
experiments  made  in  the  beginning  of  the  century  by 
Gay-Lussac.  In  examining  the  process  of  Appert  for 
the  preservation  of  animal  and  vegetable  substances — 
a  process  which  consisted  in  inclosing  these  sub- 
stances in  hermetically  sealed  vessels  and  heating 
them  afterwards  to  a  sufficiently  high  temperature — 
Gay-Lussac  had  seen,  for  example,  the  must  of  the 
grape,  which  had  been  preserved  without  alteration 
during  a  whole  year,  caused  to  enter  into  a  state  of 
fermentation  by  the  simple  fact  of  its  transference  to 
another  vessel — that  is  to  say,  by  having  been  brought 
for  an  instant  into  contact  with  the  oxygen  of  the  air. 
The  oxygen  of  the  air  appeared,  then,  to  be  iheprimum 
movem  of  fermentation. 

The  illustrious  chemists  Berzelius  and  Mitscherlich 
explained  the  phenomena  of  fermentation  otherwise. 
They  placed  these  phenomena  in  the  obscure  class 
known  as  phenomena  of  contact.  The  ferment,  in  their 
view,  took  nothing  from,  and  added  nothing  to,  the 
fermentable  matter.  It  was  an  albuminoid  substance, 
endowed  with  a  force  to  which  the  name  catalytic  was 
given.  The  ferment  in  fact  acted  by  its  mere  presence. 

A  very  curious  observation,  however,  had  been 
made  in  France  by  Cagniard-Latour  and  in  Germany 
by  Schwann.  Cagniard-Latour,  however,  was  the  first 
to  publish  this  observation,  which  was  destined  to  be- 


44  LOUIS   PASTEUR. 

come  so  fruitful.  One  of  the  ferments  most  in  use, 
and  known  as  early  as  the  leavening  of  dough  or  the 
turning  of  milk,  is  the  deposit  formed  in  beer  barrels, 
which  is  commonly  called  yeast.  Repeating  an  obser- 
vation of  the  naturalist  Leuwenhoeck,  Cagniard- 
Latour  saw  this  yeast,  which  was  composed  of  cells, 
multiplying  itself  by  budding,  and  he  proposed  to  him- 
self the  question  whether  the  fermentation  of  sugar 
was  not  connected  with  this  act  of  cellular  vegeta- 
tion. But  as  in  other  fermentations  the  existence 
of  an  organism  had  not  been  observed  even  by  the 
most  careful  search,  the  hypothesis  of  Cagniard-Latour 
of  a  possible  relation  between  the  organisation  of  the 
ferment  and  the  property  of  being  a  ferment  was 
abandoned,  though  not  without  regret  by  some 
physiologists.  M.  Dumas,  for  example,  recognised 
that  in  the  budding  of  the  yeast  globules  there  must 
be  some  clue  to  the  phenomenon  of  fermentation.  I, 
however,  repeat  that  as  nothing  of  the  kind  had  been 
found  elsewhere,  and  as  all  other  fermentations  pre- 
sented the  common  character  of  requiring,  to  put  them 
in  train,  organic  matter  in  a  state  of  decomposition, 
the  hypothesis  of  Cagniard-Latour  remained  a  simple 
incident,  instead  of  having  the  value  of  a  scientific 
principle. 

Liebig,  moreover,  carrying  general  opinion  along 
with  him,  contended  that  it  is  not  because  of  its 
being  organised  that  yeast  is  active^  but  because  of  its 


FERMENTATION.  45 

being  in  contact  with  air.  It  is  the  dead  portion  of  the 
yeast — that  which  has  lived  and  is  in  the  course  of 
alteration — which  acts  upon  the  sugar. 

The  new  memoirs  published  on  the  subject  agreed 
in  rejecting  the  hypothesis  of  any  influence  whatever 
of  organisation  or  of  life  in  the  process  of  fermentation. 
Books,  memoirs,  dogmatic  teaching,  all  were  favourable 
to  the  theoretic  ideas  of  Liebig.  If  a  few  rare  ob- 
servers indicated  the  presence  in  certain  fermentations 
of  living  organisms,  this  presence  was,  in  their  opinion, 
a  purely  accidental  fact,  which,  instead  of  favouring 
the  phenomenon  of  fermentation,  was  injurious  to  it. 

From  his  first  investigation  on  lactic  fermentation 
Pasteur  was  led  to  take  an  entirely  different  view  of 
the  matter.  In  this  fermentation  he  recognised  the 
presence  and  the  action  of  a  living  organism,  which 
was  the  ferment,  just  as  yeast  was  the  ferment  of 
alcoholic  fermentation.  The  lactic  ferment  was 
formed  of  cells,  or  rather  of  little  rods  nipped  at 
their  centres,  extremely  small,  being  hardly  the  thou- 
sandth part  of  a  millimeter  in  diameter.1  It  repro- 
duced itself  by  fission — that  is  to  say,  the  little  rod 
divided  itself  at  its  middle  and  formed  two  shorter 
rods,  which  became  elongated,  nipped,  in  their  turn, 
at  their  centres,  each  giving  rise,  as  before,  to  two  rods. 
Each  of  these,  again,  soon  divided  itself  into  two,  and 
so  on.  Why  had  not  this  been  observed  prior  to 

1    [A  millimeter  is  ^th  of  an  inch.] 


46  LOUIS  PASTEUB. 

Pasteur  ?  For  the  simple  reason  that  chemists  had 
never  observed  the  production  of  lactic  fermentation 
except  in  complex  substances.  They  mixed  chalk 
with  their  milk  for  the  purpose  of  preserving  the 
neutrality  of  the  fermenting  medium.  They  em- 
ployed substances  such  as  caserne,  gluten,  animal 
membranes,  all  of  which,  when  examined  by  the 
microscope,  exhibited  a  multitude  of  mineral  or 
organic  granules,  with  which  the  lactic  ferment  was 
confounded.  Thus  the  first  care  of  Pasteur,  with  the 
view  of  proving  the  presence  of  the  ferment  and  its 
life,  was  to  replace  the  cheesy  matter  and  all  its 
congeners  by  a  soluble,  nitrogenous  body,  which  would 
permit  of  the  microscopic  examination  of  all  the  living 
cellular  products. 

In  a  memoir  presented  to  the  Academy  of  Sciences 
hi  1857  Pasteur  stated  that  there  were  '  cases  where 
it  is  possible  to  recognise  in  lactic  fermentation,  as 
practised  by  chemists  and  manufacturers,  above  the 
deposit  of  chalk  and  the  nitrogenous  matter,  a  grey 
substance  which  forms  a  zone  on  the  surface  of  the 
deposit.  Its  examination  by  the  microscope  hardly 
permits  of  its  being  distinguished  from  the  disinte- 
grated caseum  or  gluten  which  has  served  to  start  the 
fermentation.  So  that  nothing  indicates  that  it  is  a 
special  kind  of  matter  which  had  its  birth  during  the 
fermentation.  It  is  this,  nevertheless,  which  plays  the 
principal  part.' 


FERMENTATION.  47 

To  isolate  this  substance  and  to  prepare  it  in  a 
state  of  purity,  Pasteur  boiled  a  little  yeast  with  from 
fifteen  to  twenty  times  its  weight  of  water.  He  then 
carefully  filtered  the  liquid,  dissolved  in  it  about  fifty 
grammes  of  sugar  to  the  litre,  and  added  to  it  some 
chalk.  Taking  then,  by  means  of  a  drawn-out  tube, 
from  a  good  ordinary  lactic  fermentation  a  trace  of 
the  grey  matter  of  which  we  have  just  spoken,  he 
placed  it  as  the  seed  of  the  ferment  in  the  limpid 
saccharine  solution.  By  the  next  day  a  lively  and 
regular  fermentation  had  set  in,  the  liquid  becoming 
turbid  and  the  chalk  disappearing,  and  one  could 
distinguish  a  deposit  which  progressed  continually 
as  the  chalk  dissolved.  This  deposit  was  the  lactic 
ferment. 

Pasteur  reproduced  this  experiment  by  substituting 
for  the  water  of  the  yeast  a  clear  decoction  of  nitro- 
genous plastic  substances.  The  ferment  invariably 
presented  the  same  aspect  and  the  same  multiplica- 
tion. These  results,  however,  did  not  yet  satisfy 
Pasteur.  He  desired  more  rigour  in  a  subject  of  such 
theoretic  importance.  Might  not  the  partisans  of 
Liebig's  theory  argue,  if  not  without  subtlety  yet 
with  a  semblance  of  justice,  that  the  fermentation 
was  not  due  to  the  formation  and  progressive  growth 
of  this  feeble  nitrogenous  globular  deposit,  but  rather 
to  the  nitrogenous  matter  dissolved  during  the  decoc- 
tion of  the  yeast  used  in  the  composition  of  the 


48  LOUIS  PASTEUR. 

liquor  ?  Up  to  a  certain  point  it  might  be  maintained 
that  the  dissolved  matters  which  had  been  in  contact 
with  the  oxygen  of  the  air  had  been  thrown  into  mole- 
cular motion,  that  this  motion  had  been  communicated 
to  the  fermentable  matter,  and  that  the  deposit  of  the 
pretended  organised  ferment  was  but  an  accident — 
one  of  the  physical  changes  or  one  of  the  precipitates 
so  frequently  observed  in  the  modifications  of  albumi- 
noid matters.  In  the  observation  of  Cagniard-Latour 
and  of  Schwann  as  to  the  life  of  the  yeast,  Liebig 
saw  nothing  more.  '  One  cannot  deny,'  said  he,  '  the 
organisation  of  the  yeast  or  its  multiplication  by  bud- 
ing,  but  these  living  cells  are  always  associated  with 
other  dead  cells  in  process  of  molecular  alteration. 
It  is  these  molecular  motions  which  communicate 
themselves  to  the  molecules  of  the  sugar,  break  them 
up,  and  cause  them  to  ferment.' 

The  arguments  of  Liebig  derived  great  strength 
from  the  belief  which  was  shared  by  all  chemists 
that  the  cells  of  yeast  perish  during  fermentation 
and  form  lactate  of  ammonia.  On  examining  this 
assertion,  Pasteur  found  that  not  only  was  there  no 
ammonia  formed  during  alcoholic  fermentation,  but 
that  even  if  ammonia  were  added  it  disappeared,  en 
tering  into  the  formation  of  new  yeast  cells.  Was  not 
this  a  proof  of  the  potency  of  the  organised  ferment  ? 

Tormented,  however,  by  the  idea  "that,  notwith- 
standing all   these   facts,   the  reasonings  of   Liebig 


FERMENTATION.  49 

might  still  find  some  credit,  Pasteur  worked  earnestly 
to  discover  new  facts  capable  of  demonstrating  that 
Liebig's  theory  was  absolutely  false.  He  made  two 
crucial  experiments,  the  one  relating  to  the  yeast  of 
beer,  or  of  alcohol,  and  the  other  relating  to  the  lactic 
ferment.  He  introduced  into  a  pure  solution  of  sugar 
a  small  quantity  of  crystallisable  salt  of  ammonia, 
then  some  phosphates  of  potash  and  magnesia,  and 
he  sowed  in  this  medium  an  imponderable  quantity, 
if  we  may  so  express  it,  of  fresh  cells  of  yeast.  The 
cells  thus  sown  multiplied,  and  the  sugar  fermented. 
In  other  words,  the  phosphorus,  the  potassium,  the 
magnesium  of  the  mineral  salts,  united  to  form  the 
substances  which  compose  the  ferment.  By  this  ex- 
periment, so  simple  and  yet  so  demonstrative,  the 
power  of  the  organisation  of  the  ferment  was  once 
for  all  established.  The  contact  theory  of  Berzelius 
had  no  longer  any  meaning,  since  it  was  evident  that 
the  fermentable  matter  here  furnished  to  the  ferment 
one  of  its  essential  elements,  namely,  carbon.  Liebig's 
theory  of  communicated  molecular  motion,  originating 
in  a  nitrogenous  albuminoid  substance,  had  no  better 
claim,  since  such  substances  had  been  discarded.  The 
whole  process  took  place  between  the  sugar  and  a 
ferment  germ  which  owed  its  life  and  development  to 
nutritive  matters,  the  most  important  of  which  was 
the  fermentable  substance.  Fermentation,  in  short, 
was  simply  a  phenomenon  of  nutrition.  The  ferment 


50  LOUIS  PASTEUR. 

augmented  in  weight,  feeding  upon  the  sugar,  and  its 
vitality  was  such  that  it  contrived  to  build  up  the 
complex  materials  of  its  own  organisation  by  means 
of  sugar  and  purely  mineral  elements. 

In  a  second  experiment,  Pasteur  demonstrated 
that,  notwithstanding  their  smallness  and  the  pos- 
sibility of  confounding  them  with  the  amorphous 
granules  of  caseine  and  gluten,  the  little  particles  of 
lactic  ferment  were  indeed  alive,  and  that  they,  and 
they  only,  were  the  cause  of  lactic  fermentation.  He 
mixed  with  some  water,  sweetened  with  sugar,  a  small 
quantity  of  a  salt  of  ammonia,  some  alkaline  and 
earthy  phosphates,  and  some  pure  carbonate  of  lime 
obtained  by  precipitation.  At  the  end  of  twenty-four 
hours  the  liquid  began  to  get  turbid  and  to  give  off 
gas.  The  fermentation  continued  for  some  days. 
The  ammonia  disappeared,  leaving  a  deposit  of  phos- 
phates and  calcareous  salt.  Some  lactate  of  lime  was 
formed,  and  at  the  same  time  one  could  notice  the 
deposition  of  the  little  lactic  ferment.  The  germs  of 
the  lactic  ferment  had,  in  this  case,  been  derived  from 
particles  of  dust  adhering  to  the  substances  themselves, 
of  which  the  mixtures  were  made,  or  to  the  vessels 
used,  or  from  the  surrounding  air.  The  chapter  on 
spontaneous  generation  will  render  this  clear. 

It  suffices  here  to  state  that  the  results  of  this 
second  experiment  were  absolutely  conclusive,  and 
that  the  theories  of  contact  force  or  of  communicated 


FEEMENTATION.  51 

motion,  which  up  to  that  time  had  reigned  in  ccience, 
were  completely  overthrown. 


II. 

The  light  shed  by  these  experiments  quickly  ex- 
tended its  sphere  ;  and  Pasteur  lost  no  time  in  dis- 
covering a  new  ferment,  that  of  butyric  acid.  Having 
shown  the  absolute  independence  which  exists  between 
the  ferment  of  butyric  acid  and  the  others,  he  found, 
contrary  to  the  general  belief,  that  the  lactic  ferment  is 
incapable  of  giving  rise  to  butyric  acid,  and  that  there 
exists  a  butyric  fermentation  having  its  own  special 
ferment.  This  ferment  consists  of  a  species  of  vibrio. 
Little  transparent  cylindrical  rods,  rounded  at  their  ex- 
tremities, isolated  or  united  in  chains  of  two  or  three,  or 
sometimes  even  more,  form  these  vibrios.  They  move  by 
gliding,  the  body  straight,  or  bending  and  undulating. 
They  reproduce  themselves  by  fission,  and  to  this  mode 
of  generation  their  frequent  arrangement  in  the  form 
of  a  chain  is  due. 

Sometimes  one  of  the  little  rods,  with  a  train  of 
others  behind  it,  agitates  itself  in  a  lively  manner  as  if 
to  detach  itself  from  the  rest.  Often,  also,  the  little 
rod,  after  being  broken  off,  holds  on  still  to  its  chain 
by  a  mucous  transparent  thread. 

These  little  infusoriae  may  be  sown  like  the  yeast 
of  beer  or  the  lactic  ferment.  If  the  medium  in 


52  LOUIS  PASTEUR. 

which  they  are  sown  is  suitable  for  their  nourishment, 
they  will  multiply  to  infinity ;  but  the  character  most 
essential  to  be  observed  is,  that  they  may  be  sown  in  a 
liquid  which  contains  only  ammonia  and  crystallisable 
substances,  together  with  the  fermentable  substances, 
sugar,  lactic  acid,  gum,  &c.  The  butyric  fermentation 
manifests  itself  as  these  little  organisms  multiply. 
Their  weight  sensibly  increases,  though  it  is  always 
minute  in  comparison  with  the  quantity  of  butyric 
acid  produced ;  this  is  found  to  be  the  case  in  all 
other  fermentations. 

This  experiment  no  doubt  resembles  those  made 
with  the  alcoholic  and  lactic  ferments.  But  it  is  dis- 
tinguished from  them  by  one  circumstance  eminently 
worthy  of  attention.  The  butyric  ferment,  by  its 
motions  and  by  its  mode  of  generation,  furnishes  the 
irrefutable  proof  of  its  organisation  and  of  its  life. 
This  ferment,  moreover,  presented  to  Pasteur  a  new 
and  unexpected  peculiarity.  The  vibrios  live  and 
multiply  without  the  smallest  supply  of  air  or  of  free 
oxygen.  Not  only,  indeed,  do  they  live  without  air, 
but  the  air  destroys  them  and  arrests  the  fermentation 
which  they  initiate.  If  a  current  of  pure  carbonic 
acid  is  made  to  pass  into  the  liquid  where  they  are 
multiplying,  their  life  and  reproduction  do  not  appear 
to  be  at  all  affected  by  it.  If,  on  the  contrary,  instead 
of  the  current  of  carbonic  acid  we  employ  one  of 
atmospheric  air  for  only  one  or  two  hours,  the  vibrios 


FERMENTATION.  53 

fall  without  movement  to  the  bottom  of  the  vessel,  and 
the  butyric  fermentation  which  was  dependent  on  their 
existence  is  immediately  arrested. 

Pasteur  designated  this  new  class  of  organisms  by 
the  name  of  anaerobies  ;  that  is  to  say,  beings  which 
can  live  without  air.  He  reserves  the  designation 
aerobics  for  all  the  other  microscopic  beings  which,  like 
the  larger  animals,  cannot  live  without  free  oxygen. 
*  It  matters  little,'  added  Pasteur,  '  whether  the  pro- 
gress of  science  makes  of  this  vibrio  a  plant  or  an 
animal ;  it  is  a  living  organism,  endowed  with  motion, 
which  is  a  ferment  and  which  lives  without  air.' 

In  meditating  upon  these  facts,  and  upon  the 
general  character  of  fermentation,  Pasteur  soon  found 
himself  in  a  position  to  approach  more  nearly  to  the 
essential  nature  of  these  mysterious  phenomena.  In 
what  way  do  microscopic  organisms  provoke  the  phe- 
nomena of  fermentation  ? 

The  organism  eats,  if  one  may  say  so,  one  part  of 
the  fermentable  matter.  But  how  does  this  phenome- 
non of  nutrition  differ  so  much  from  that  of  higher 
beings  ?  In  general,  for  a  given  weight  of  nutritive 
matter  which  the  animal  takes  in,  it  assimilates  a 
quantity  of  the  same  order.  In  fermentation,  on  the 
contrary,  the  ferment,  while  nourishing  itself  with 
fermentable  matter,  decomposes  a  quantity  great  in 
comparison  to  its  own  individual  weight.  Again,  the 


54  LOUIS  PASTEUK. 

butyric  ferment  lives  without  free  oxygen.  Is  there 
not,  said  Pasteur,  a  hidden  relation  between  the 
property  of  being  a  ferment  and  the  faculty  of  living 
without  free  oxygen?  Are  not  vibrios  which  impera- 
tively require  for  their  nutrition  and  multiplication  the 
presence  of  oxygen  gas  those  which  will  never  have  the 
properties  of  ferments  ? 

Pasteur  then  contrived  a  series  of  experiments  with 
the  view  of  placing  in  parallelism  these  two  curious 
physiological  facts:  life  without  air  and  the  charac- 
teristics of  ferments. 

We  know  how  wine  and  beer  are  prepared.  The 
must  of  grapes  and  the  must  of  beer  are  placed  in 
wooden  vats,  or  in  barrels  of  greater  or  less  dimen- 
sions. Whether  the  fermentation  proceeds  from  germs 
taken  from  the  exterior  surface  of  the  grapes,  or 
from  a  small  quantity  of  ferment  sown  in  the  must 
under  the  form  of  yeast,  as  in  the  fermentation  of 
beer,  the  life  of  the  ferment,  its  multiplication,  the 
augmentation  of  its  weight,  are  so  many  vital  actions 
which  to  a  certainty  cannot  borrow  from  the  free 
oxygen  of  the  external  air,  or  from  that  originally 
dissolved  in  the  must,  an  appreciable  quantity  of  this 
gas.  All  the  life  of  the  cells  of  the  ferment  which 
multiplies  itself  indefinitely  appears  then  to  take  place 
apart  from  free  oxygen  gas.  In  certain  breweries 
in  England  the  fermenting  vats  have  sometimes  a 
capacity  of  several  thousands  of  hectolitres  ;  and  the 


FERMENTATION.  55 

fermentation  liberates  pure  carbonic  acid,  a  gas  much 
heavier  than  atmospheric  air,  which  rests  on  the 
surface  of  the  liquid  in  the  vat  in  a  layer  thick  enough 
to  protect  the  liquid  underneath  from  any  contact  with 
the  external  air.  All  this  liquid  mass,  then,  is  inclosed 
between  the  wooden  sides  of  the  vat  and  a  deep  layer 
of  heavy  gas  which  contains  no  trace  of  free  oxygen. 
In  this  liquid,  nevertheless,  the  life  of  the  cells  of  the 
ferment  and  the  production  of  all  its  constituents  go 
on  for  several  days  with  extraordinary  activity.  Here 
certainly  we  have  life  without  air,  and  the  ferment 
character  expresses  itself  in  the  enormous  difference 
between  the  weight  of  the  ferment  formed  and  collected 
from  the  vats  under  the  name  of  yeast,  at  the  end 
of  the  operation,  and  the  weight  of  the  sugar  which 
has  fermented,  transforming  itself  into  alcohol,  car- 
bonic acid,  and  various  other  products. 

Pasteur  has  studied  experimentally  that  which 
takes  place  when,  without  otherwise  changing  the 
conditions  of  these  phenomena,  the  arrangement 
is  so  modified  as  to  permit  the  introduction  of  the 
free  oxygen  of  the  atmosphere.  It  sufficed  for  this 
purpose  to  provoke  a  fermentation  of  the  must  of 
beer,  or  the  must  of  grapes,  upon  shallow  glass  dishes 
presenting  a  large  surface,  or  in  a  flat-bottomed 
wooden  trough  with  sides  a  few  centimeters  in  height, 
instead  of  in  deep  vats  as  before.  In  these  new  con- 
ditions the  fermentation  manifests  an  activity  even 
5 


56  LOUIS  PASTEUE. 

more  extraordinary  than  it  did  in  the  deep  vats.  The 
life  of  the  ferment  is  itself  singularly  enhanced,  but 
the  proportion  of  the  weight  of  the  decomposed  sugar 
to  that  of  the  yeast  formed  is  absolutely  different  in 
the  two  cases.  While,  for  example,  in  the  deep  vats, 
a  kilogram  of  ferment  sometimes  decomposes  seventy, 
eighty,  one  hundred,  or  even  one  hundred  and  fifty 
kilograms  of  sugar,  in  the  shallow  troughs  one  kilo- 
gram of  the  ferment  will  be  found  to  correspond  to 
only  five  or  six  kilograms  of  decomposed  sugar.  These 
proportions  between  the  weight  of  the  sugar  which 
ferments  and  the  weight  of  the  ferment  produced, 
constitute  the  measure  of  what  one  might  call  the 
ferment's  character — of  that  character  which  distin- 
guishes its  mode  of  life  from  that  of  all  other  existences, 
great  or  small,  in  which  the  weight  of  the  organising 
matter  and  the  assimilated  alimentary  matter  are  about 
equal.  In  other  words,  the  more  free  oxygen  the  yeast 
ferment  consumes,  the  less  is  its  power  as  a  ferment. 
Such  is  the  case  in  the  shallow  troughs  where  the 
extended  surface  is  exposed  to  the  contact  of  the 
oxygen  of  the  air.  The  more,  on  the  contrary,  the 
life  of  the  ferment  is  carried  on  without  the  presence  of 
free  oxygen,  the  greater  is  its  power  of  decomposing  and 
of  fermenting  the  saccharine  matter.  This  is  the  case 
in  deep  casks.  The  intimate  co-relation  then  between 
life  without  air  and  fermentation  appears  complete. 
The  unexpected  light  which  these  facts  threw  upon 


FERMENTATION.  57 

the  cause  of  the  phenomena  of  fermentation  made  a 
forcible  impression  upon  all  thinking  minds.  '  In 
these  infinitely  small  organisms,'  M.  Dumas  said  one 
day  to  M.  Pasteur  before  the  Academy  of  Sciences, 
'  you  have  discovered  a  third  kingdom — the  kingdom 
to  which  those  organisms  belong  which,  with  all  the 
prerogatives  of  animal  life,  do  not  require  air  for  their 
existence,  and  which  find  the  heat  that  is  necessary 
for  them  in  the  chemical  decompositions  which  they 
set  up  around  them.' 

The  work  of  Pasteur,  demonstrating  that  fermen- 
tation was  always  dependent  on  the  life  of  a  micro- 
scopic organism,  continued  without  interruption.  One 
of  the  most  remarkable  of  his  researches  is  that 
which  relates  to  the  fermentation  of  the  tartrate  of 
lime.  The  demonstration  of  life  and  of  fermentation 
without  free  oxygen  is  in  this  paper  carried  to 
the  utmost  limits  of  experimental  rigour  and  pre- 
cision. 

in. 

But  there  is  still  another  class  of  chemical  pheno- 
mena where  the  life  without  air  of  microscopic  or- 
ganisms is  fully  shown.  Pasteur  -proved  that  in  the 
special  fermentation  which  bears  the  name  of  putre- 
faction the  primum  movens  of  the  putrefaction  resides 
in  microscopic  vibrios  of  absolutely  the  same  order 
as  those  which  compose  the  butyric  ferment.  The 


58  LOUIS  PASTEUR. 

fermentation  of  sugar,  of  mannite,  of  gums,  of  lactate 
of  lime,  by  the  butyric  vibrio,  so  closely  resembles  the 
phenomena  of  putrefaction,  that  one  might  call  these 
fermentations  the  putrefaction  of  sugar  and  of  the 
other  products. 

If  it  has  been  thought  right  to  call  the  fermenta- 
tion of  animal  matters  putrefaction,  it  is  because  at  the 
moment  of  the  decomposition  of  fibrine,  of  albumen, 
of  blood,  of  gelatine,  of  the  substance  of  the  tendons, 
&c.,  the  sulphur,  and  even  the  phosphorus,  which 
enter  into  their  composition  give  rise  to  putrid  odours, 
due  to  the  evil-smelling  gases  of  sulphur  and  phos- 
phorus. 

The  phenomena  of  putrefaction  being  then  simply 
fermentations,  differing  only  in  regard  to  the  chemical 
composition  of  the  fermenting  matters,  Liebig  natu- 
rally included  them  in  his  general  theory  of  the  de- 
composition of  organic  matters  after  death.  At  a 
period  long  antecedent  to  Pasteur's  labours  it  had 
been  established  that  there  existed  in  putrefying 
matters  fungi  or  microscopic  animalcules,  and  the  idea 
had  taken  shape  that  these  creatures  might  have  an 
influence  in  the  phenomena.  The  proofs  were  want- 
ing, but  the  notioji  of  a  possible  relation  remained. 
We  may  read  in  his  '  Lessons  on  Chemistry '  with 
what  disdain  Liebig  mentioned  these  hypothetical 
opinions. 

'  Those  who  pretend  to  explain  the  putrefaction 


FERMENTATION.  59 

of  animal  substances  by  the  presence  of  animalcules,' 
he  wrote,  '  reason  very  much  like  a  child  who  would 
explain  the  rapidity  of  the  Ehine  by  attributing  it 
to  the  violent  motions  imparted  to  it  in  the  direc- 
tion of  Bingen  by  the  numerous  wheels  of  the  mills 
of  Mayence.  Is  it  possible  to  consider  plants  and 
animals  as  the  causes  of  the  destruction  of  other 
organisms  when  their  own  elements  are  condemned  to 
undergo  the  same  decompositions  as  the  creatures 
which  have  preceded  them?  If  the  fungus  is  the 
cause  of  the  destruction  of  the  oak,  if  the  microscopic 
animalcula  is  the  cause  of  the  putrefaction  of  the 
dead  elephant,  I  would  ask  in  my  turn  what  is  the 
cause  which  determines  the  putrefaction  of  the  fungus 
or  of  the  microscopic  animalcula  when  life  is  with- 
drawn from  these  two  organisms  ? ' 

Thirty-two  years  later,  and  after  Pasteur  had 
accumulated,  during  more  than  twenty  years,  proof 
upon  proof  that  the  theory  of  Liebig  would  not  stand 
examination,  a  physician  of  Paris,  M.  Bouillaud,  asked, 
with  the  insistent  voice  of  a  querulous  octogenarian : 
'  Let  M.  Pasteur  then  tell  us  here,  in  presence  of  the 
Academie  de  Medecine,  what  are  the  ferments  of  the 
ferments.' 

Before  replying  to  this  argument,  which  Liebig 
and  M.  Bouillaud  believed  to  be  irrefutable,  Pasteur, 
wishing  to  mark  all  the  phases  of  the  phenomena, 
expounded  in  a  short  preamble  the  part  played  by 


60  LOUIS  PASTEUE. 

atmospheric  oxygen  in  the  destruction  of  animal  and 
vegetable  matters  after  death.  It  is  easy  to  under- 
stand, indeed,  that  fermentation  and  putrefaction  only 
represent  the  first  phase  of  the  return  to  the  atmo- 
sphere and  to  the  soil  of  all  that  has  lived.  Fermenta- 
tions and  putrefactions  give  rise  to  substances  which 
are  still  very  complex,  although  they  represent  the 
products  of  decomposition  of  fermentable  matters. 
When  sugar  ferments,  a  large  proportion  of  it  becomes 
gas  ;  but  alongside  of  the  carbonic  acid  gas  which 
is  formed,  and  which  is,  indeed,  a  partial  return  of 
the  sugar  to  the  atmosphere,  new  substances,  such 
as  alcohol,  succinic  acid,  glycerine,  and  materials  of 
yeast,  are  produced.  When  the  flesh  of  animals 
putrifies,  certain  products  of  decomposition,  also  very 
complex,  are  formed  with  the  vapour  of  water  and 
the  other  gases  of  putrefaction.  Where,  then,  does 
nature  find  the  agents  of  destruction  of  these  secondary 
products  ? 

The  great  fact  of  the  destruction  of  animal  and 
vegetable  matters  is  accomplished  by  slow  combustion, 
through  the  appropriation  of  atmospheric  oxygen. 
Here,  again,  one  must  banish  from  science  the  pre- 
conceived views  which  assumed  that  the  oxygen  seized 
directly  on  the  organic  matter  after  death,  and  that 
this  matter  was  consumed  by  purely  chemical  pro- 
cesses. It  is  life  that  presides  over  this  work  of  death. 

If  fermentation  and  putrefaction  are  principally 


FERMENTATION.  61 

the  work  of  microscopic  anaerobies,  living  without  free 
oxygen,  the  slow  combustion  is  found  very  largely,  if 
not  exclusively,  to  depend  upon  a  class  of  infinitely 
small  aerobics.  It  is  these  last  which  have  the  pro- 
perty of  consuming  the  oxygen  of  the  air.  It  is  these 
lower  organisms  which  are  the  powerful  agents  in 
the  return  to  the  atmosphere  of  all  which  has  lived. 
Mildew,  mould,  bacteria,  which  we  have  already 
noticed,  monads,  two  thousand  of  which  would  go  to 
make  up  a  millimeter,  all  these  microscopic  organisms 
are  charged  with  the  great  work  of  re-establishing  the 
equilibrium  of  life  by  giving  back  to  it  all  that  it 
has  formed. 

To  demonstrate  the  important  part  played  every- 
where by  these  microscopic  organisms,  Pasteur  made 
two  experiments.  He  first  introduced  into  vessels  air 
deprived  of  all  dust.  This  process  we  shall  have  occa- 
sion to  examine  in  all  its  details,  in  connection  with 
the  researches  on  spontaneous  generation.  In  these 
vessels,  containing  pure  air,  were  placed  the  water  of 
yeast  with  sugar  dissolved  in  it,  milk,  sawdust — all 
of  which,  had  been  deprived  by  heat  of  the  germs  of 
the  lower  organisms.  The  vessels  and  their  contents 
were  then  subjected  to  a  temperature  of  twenty- 
five  to  thirty-five  degrees  Centigrade.  In  a  series 
of  parallel  experiments,  made  under  the  same  con- 
ditions and  at  the  same  temperature,  Pasteur  took 
no  steps  to  prevent  the  germination  of  the  little  seeds 


62  LOUIS  PASTEUR. 

of  mould  suspended  in  the  air,  or  associated  with  the 
substances  contained  in  the  vessels,  neither  did  he 
avoid  other  infinitely  small  germs  of  the  class 
aerobies. 

After  some  time  the  air  of  all  the  vessels  of  the 
two  series  was  submitted  to  analysis,  when,  behold,  a 
very  interesting  fact !  In  the  vessels  where  life  had 
been  withdrawn  from  the  organic  matters — that  is 
to  say,  where  there  were  no  germs — the  air  still  con- 
tained a  large  proportion  of  oxygen.  In  the  vessels, 
on  the  contrary,  where  the  microscopic  organisms 
had  been  allowed  to  develop,  the  oxygen  was  totally 
absent,  having  been  replaced  by  carbonic  acid  gas. 
And,  further,  for  this  absorption  and  total  consumption 
of  the  oxygen  gas  a  few  days  had  sufficed ;  while  in  the 
vessels  without  microscopic  life  there  remained,  after 
several  years,  a  considerable  quantity  of  oxygen  in  a 
free  state,  so  weak  is  the  proportion  of  oxygen  that 
the  organic  matters  consume  directly  and  chemically 
when  the  infinitely  small  organisms  are  absent. 

But  can  these  microscopic  organisms,  after  having 
decomposed  or  burnt  up  all  these  secondary  products, 
be  in  their  turn  decomposed  ? 

How,  cried  M.  Bouillaud,  repeating  his  question, 
can  they  be  destroyed  or  decomposed?  How  can 
their  materials,  which  are  of  the  same  order  as  those 
of  all  the  living  creatures  of  the  earth,  be  gasified  and 
caused  to  return  to  the  atmosphere  ?  After  having 


FERMENTATION.  63 

been  charged  with  the  transformation  of  others,  whose 
business  will  it  be  to  transform  them  ? 

A  ferment  which  has  finished  its  work,  replied 
Pasteur,  and  which  for  want  of  aliment  cannot  con- 
tinue it,  becomes  in  its  turn  an  accumulation,  so  to 
speak,  of  dead  organic  matters.  Such,  for  example, 
would  be  an  accumulation  of  yeast  exposed  to  the  air. 
Leave  this  mass  to  itself  in  summer  temperature,  and 
you  will  see  appear  in  the  interior  of  the  mass  ana- 
erobic vibrios  and  the  putrefactions  associated  with 
their  life  when  protected  from  contact  with  the  air.  At 
the  same  time,  on  the  surface  of  the  entire  mass — that 
is  to  say,  that  which  finds  itself  in  immediate  contact 
with  the  oxygen  of  the  air — the  germs  of  bacteria,  the 
seeds  of  mould  will  grow,  and,  by  fixing  the  oxygen, 
determine  the  slow  combustions  which  gasify  the  mass. 
The  ferments  of  ferments  are  simply  ferments.  As 
long  as  the  aerobic  ferments  of  the  surface  have  at 
their  disposal  free  oxygen,  they  will  multiply  and  con- 
tinue their  work  of  destruction.  The  anaerobic  vibrios 
perish  for  want  of  new  matter  to  decompose,  and  they 
form,  in  their  turn,  a  mass  of  organic  matter  which,  by 
and  by,  becomes  the  prey  of  aerobies.  The  portion  of 
the  aerobies  which  has  lived  becomes  the  prey  either 
of  new  aerobies  of  different  species,  or  of  individuals 
of  their  own  species,  so  that  from  putrefaction  to 
putrefaction,  and  from  combustion  to  combustion,  the 
organic  mass  with  which  we  started  finds  itself  reduced 


64  LOUIS  PASTEUR. 

to  an  assemblage  of  anaerobic  and  aerobic  germs — of 
those  same  germs  which  were  mixed  up  in  the  original 
primitive  organic  substances. 

Though  a  collection  of  germs  becomes  again  in  its 
turn  a  collection  of  organic  matter,  subject  to  the 
double  action  of  the  phenomena  of  putrefaction  and 
of  combustion,  there  need  be  no  anxiety  as  to  their 
ultimate  destruction ;  in  the  final  analysis  they  repre- 
sent life  under  its  eternal  form,  for  life  is  the  germ, 
and  the  germ  is  life. 

Thus  in  the  destruction  of  that  which  has  lived, 
all  reduces  itself  to  the  simultaneous  action  of  these 
three  great  natural  phenomena — fermentation,  putre- 
faction, and  slow  combustion.  A  living  organism 
dies — animal,  or  plant,  or  the  remains  of  one  or  the 
other.  It  is  exposed  to  the  contact  of  the  air.  To  the 
life  which  has  quitted  it  succeeds  life  under  other 
forms.  In  the  superficial  parts,  which  the  air  can 
reach,  the  germs  of  the  infinitely  small  aerobics  hatch 
and  multiply  themselves.  The  carbon,  the  hydrogen, 
and  the  nitrogen  of  the  organic  matters  are  trans- 
formed by  the  oxygen  of  the  air,  and  under  the  in- 
fluence of  the  life  of  these  aerobics,  into  carbonic 
acid,  vapour  of  water,  and  ammonia  gas.  As  long  as 
organic  matter  and  air  are  present,  these  combustions 
will  continue.  While  these  superficial  combustions 
are  going  on,  fermentation  and  putrefaction  are  doing 


FERMENTATION.  65 

their  work  in  the  interior  of  the  mass  by  the  developed 
germs  of  the  anaerobies,  which  not  only  do  not  require 
oxygen  for  their  life,  but  which  oxygen  actually  kills. 
Little  by  little,  at  length,  by  this  work  of  fermentation 
and  slow  combustion,  the  phenomenon  is  accomplished. 
Whether  in  the  free  atmosphere,  or  under  the  earth, 
which  is  always  more  or  less  impregnated  with  air,  all 
animal  and  vegetable  matters  end  by  disappearing. 
To  arrest  these  phenomena  an  extremely  low  tem- 
perature is  required.  It  is  thus  that  in  the  ice  of  the 
Polar  regions  antediluvian  elephants  have  been  found 
perfectly  intact.  The  microscopic  organisms  could  not 
live  in  so  cold  a  temperature.  These  facts  still  further 
strengthen  all  the  new  ideas  as  to  the  important  part 
performed  by  these  infinitely  small  organisms,  which 
are,  in  fact,  the  masters  of  the  world.  If  we  could 
suppress  their  work,  which  is  always  going  on,  the 
surface  of  the  globe,  encumbered  with  organic  matters, 
would  soon  become  uninhabitable. 


66  LOUIS  PASTEUE. 


ACETIC    FERMENTATION. 

THE    MANUFACTURE    OF   VINEGAR. 

SOON  afterwards  Pasteur  came  upon  a  most  curious 
illustration  of  the  '  fixation '  of  atmospheric  oxygen  by 
a  microscopic  organism — the  transformation  of  wine 
into  vinegar.  As  its  name  indicates,  vinegar  is 
nothing  else  than  wine  turned  sour.  Everybody 
has  remarked  that  wine,  left  to  itself,  in  circum- 
stances which  occur  daily,  is  frequently  transformed 
into  vinegar.  This  is  noticed  more  particularly 
when  bottles,  having  been  uncorked,  are  left  in  a 
half-empty  condition.  Sometimes,  however,  wine 
turns  sour  even  in  corked  bottles.  In  this  case 
we  may  be  sure  that  the  bottles  have  been  standing 
upright,  and  that  corks  more  or  less  defective  have 
permitted  the  air  to  penetrate  into  the  wine.  The 
presence  of  air,  in  fact,  is  indispensable  to  the  chemical 
act  of  transforming  wine  into  vinegar.  How  does  this 
air  intervene  ?  And  what  is  the  little  microscopic 
creature  which,  in  conjunction  with  the  air,  becomes 
the  agent  of  this  fermentation  ? 


ACETIC  FERMENTATION.  67 

In  a  celebrated  lecture  given  at  Orleans  at  the 
request  of  the  manufacturers  of  vinegar  in  that  town, 
Pasteur,  after  having  stated  the  two  foregoing  scien- 
tific questions,  proceeded  to  examine  the  difference 
between  wine  and  vinegar.  What  takes  place  in  the 
fermentation  of  the  juice  of  the  grape  which  yields  the 
wine  ?  The  sugar  of  this  juice  disappears,  giving 
place  to  carbonic  acid  gas,  which  is  exhaled  during 
fermentation,  and  to  alcohol,  which  remains  in  the 
fermented  liquid.  Formerly,  chemists  gave  the  name 
of  '  spirit '  to  all  volatile  matters  which  could  be 
collected  from  distillation.  Now,  when  we  distil  wine 
and  condense  the  vapour  in  a  worm  surrounded  by 
cold  water,  we  collect  the  spirit  of  wine  at  the  ex- 
tremity of  the  worm — this,  when  the  water  with 
which  it  is  mixed  during  distillation  is  withdrawn  from 
it,  we  designate  by  the  name  of  alcohol.  Vinegar 
contains  no  alcohol.  When  distilled  it  yields  water 
and  a  spirit.  But  this  spirit  is  acid,  with  a  very 
pungent  odour,  and  not  inflammable  like  spirit  of 
wine.  Separated  from  the  water  which  had  accom- 
panied it  during  the  distillation,  this  spirit  takes  the 
name  of  acetic  acid.  This  is  the  form  in  which  it  is 
used  in  smelling  bottles — in  those  bottles  of  English 
salts  the  vapour  of  which  is  so  penetrating. 

In  the  formation  of  vinegar  in  contact  with  air 
the  alcohol  disappears,  and  is  replaced  by  acetic  acid. 
The  air  has  thus  given  up  something  to  the  wine. 


68  LOUIS  PASTEUR. 

Atmospheric  air  every  one  knows  to  be  a  mixture 
of  nitrogen  and  oxygen,  the  nitrogen  in  the  proportion 
of  four-fifths  of  the  total  volume,  and  the  oxygen  of 
one-fifth.  Well,  in  the  transformation  of  wine  into 
vinegar  the  nitrogen  remains  inactive.  It  is  the 
oxygen  alone  which  enters  into  combination  with  the 
alcohol.  You  ask  for  the  proof  of  this?  Take  a 
bottle  of  wine  turned  sour,  a  bottle  which  at  the  same 
time  is  stopped  hermetically  ;  if  the  oxygen  of  the  air 
contained  in  the  bottle  has  combined  with  the  alcohol, 
then,  instead  of  air,  there  will  be  nothing  in  the  bottle 
but  nitrogen  gas.  Turn  the  bottle  upside  down  and 
open  it  in  a  basin  of  water.  The  water  of  the  basin 
will  rush  into  the  bottle  to  fill  the  partial  vacuum 
created  by  the  disappearance  of  the  oxygen.  The 
volume  of  water  which  enters  the  bottle  is  precisely 
equal  to  a  fifth  part  of  the  total  original  volume  of 
the  air  which  the  bottle  contained  at  the  time  when 
it  was  closed.  Moreover,  it  is  easy  to  show  that  the 
gas  which  remains  in  the  bottle  has  the  properties  of 
nitrogen  gas.  A  lighted  match  is  extinguished  in  it 
as  if  plunged  into  water,  and  a  bird  dies  immediately 
in  it  of  asphyxia. 

If  we  confine  our  knowledge  to  what  has  gone 
before,  it  would  seem  that  alcohol  diluted  with  water 
and  exposed  to  the  air  ought  to  furnish  acetic  acid. 
It  is  not  so,  however.  Pure  water  alcoholised  to  the 
degree  of  ordinary  wines  may  remain  for  whole  years 


ACETIC  FERMENTATION.  69 

in  contact  with  the  air,  without  the  least  acetifica- 
tion.  In  this  difference  between  natural  wine  and  pure 
water  alcoholised,  and  exposed  to  contact  with  air,  we 
touch  upon  a  vital  point  in  the  phenomena  of  fermen- 
tation. The  celebrated  theory  of  Liebig,  which  Pas- 
teur was  destined  to  overthrow,  might  be  thus  summed 
up  : — If  pure  alcoholised  water  cannot  become  sour  in 
contact  with  air,  as  is  the  case  with  wine,  it  is  because 
the  pure  alcoholised  water  lacks  the  albuminoid  sub- 
stance which  exists  in  the  wine  in  a  state  of  chemical 
alteration,  and  which  is  a  ferment  capable  of  causing 
the  oxygen  of  the  air  to  combine  with  the  alcohol. 
And  the  proof,  according  to  Liebig,  that  things  act 
rigorously  thus  is,  that  if  you  add  to  the  mixture  of 
water  and  alcohol  a  little  flour,  or  a  little  meat-juice, 
or  even  a  minute  quantity  of  any  vegetable  juice, 
the  acetic  fermentation  arises,  as  if  by  compulsion. 
In  other  words,  by  the  addition  of  a  small  quantity 
of  any  nitrogenised  substance  in  process  of  alteration, 
you  cause  the  union  of  the  oxygen  of  the  air  with  the 
alcohol. 

There  is  doubtless  always  in  the  wine,  when  it 
turns  sour,  a  necessary  intermediary,  producing  the 
fixation  of  the  oxygen  of  the  air  ;  since  hi  no  circum- 
stances can  pure  alcohol,  diluted  to  any  degree  what- 
ever with  pure  water,  transform  itself  into  vinegar. 
But  this  necessary  intermediary  is  not,  as  the  German 
theory  would  have  it,  a  dead  albuminoid  substance ; 


70  LOUIS  PASTEUE. 

it  is  a  plant,  and  of  all  plants  one  of  the  simplest  and 
most  minute,  which  has  been  known  from  time  imme- 
morial under  the  name  of  flower  of  vinegar.  This 
little  fungus  is  invariably  present  on  the  surface  of 
a  wine  which  is  being  transformed  into  vinegar. 
Liebig  was  not  ignorant  of  this,  but  he  regarded  it  as 
a  simple  coincidence.  Do  we  not  know,  said  he,  that 
whenever  an  infusion  of  organic  matter  is  exposed  to 
the  air  it  becomes  covered  with  a  cryptogamic  vege- 
tation, or  is  invaded  by  a  crowd  of  animalcules  ?  Is 
not  vinegar  a  vegetable  infusion  ?  Vinegar  affords  a 
refuge  to  the  flower  of  vinegar,  just  as  it  gives  refuge 
to  what  are  called  the  little  eels  of  vinegar. 

We  can  appreciate  here  the  uncertainties  of  pure 
observation.  The  great  art — and  no  one  practised  it 
better  than  Pasteur — consists  in  instituting  decisive 
experiments  which  leave  no  room  for  an  inexact  inter- 
pretation of  facts.  These  decisive  proofs  of  the  true 
part  played  by  the  little  microscopic  fungus,  by  this 
flower  of  vinegar,  this  mycoderma  aceti,  are  thus 
formulated  by  Pasteur.  It  is  but  another  example 
of  the  method  which  he  used  in  alcoholic,  lactic,  and 
tartaric  fermentations.  The  theories  of  Berzelius,  of 
Mitscherlich,  and  of  Liebig  were  destined  again  to 
receive  the  rudest  shocks  by  the  demonstration  of  these 
rigorous  facts. 

Let  us  place  a  little  wine  in  a  bottle,  then  her- 
metically seal  it,  and  leave  it  to  itself.  In  these 


ACETIC  FERMENTATION.  71 

conditions  the  wine  becomes  sour.  But  if  we  take 
the  precaution  of  putting  the  bottle  into  hot  water,  so 
that  the  wine  and  the  air  in  the  bottle  may  be  heated 
for  some  instants  to  a  temperature  of  60°  Centigrade, 
and  if,  after  cooling,  we  leave  the  bottle  to  itself, 
the  wine  in  these  conditions  will  never  become  trans- 
formed into  vinegar.  The  heating,  however,  must 
have  left  intact  the  albuminoid  or  nitrogenous  sub- 
stances contained  in  the  wine.  These,  then,  cannot 
constitute  the  ferment  of  the  vinegar.  Can  it  be 
maintained  that  by  heating  the  wine  to  60°  we  have 
altered  the  albuminoid  matter,  which  is,  on  this 
account,  no  longer  able  to  act  as  a  ferment,  or,  in  other 
words,  no  longer  able  to  determine  the  union  of  the 
oxygen  of  the  air  with  the  alcohol  ?  This  hypo- 
thesis falls  to  pieces  before  the  following  experiment. 
Open  the  bottle,  blow  into  it  with  bellows,  so  that 
the  once  heated  wine  shall  come  into  contact  with 
ordinary  air,  and  the  acetification  of  the  wine  will  take 
place. 

But  the  master  experiment  is  the  following.  We 
have  seen  that  pure  alcoholised  water  never  turns  sour 
unless  some  albuminoid  matter  is  introduced  into  it. 
Pasteur  saw  that  this  albuminoid  matter  might  be 
completely  suppressed  and  replaced  by  saline  crystal- 
lisable  substances,  alkaline  and  earthy  phosphates,  to 
which  has  been  added  a  little  phosphate  of  ammonia. 
In  these  conditions,  especially  if  the  alcoholised  water 


72  LOUIS  PASTEUR. 

be  acidulated  by  small  quantities  of  pure  acetic  acid, 
one  actually  sees  the  mycoderm  developing,  and  the 
alcohol  transforming  itself  into  acetic  acid.  It  is 
not  possible  to  demonstrate  in  a  more  convincing 
manner  that  the  albuminoid  matters  of  the  wine  are 
not  in  this  case  the  acetic  ferment.  These  albuminoid 
matters,  however,  contribute  to  the  acetic  fermenta- 
tion, but  only  as  being  an  aliment  to  the  mycoderma 
aceti,  and  notably  a  nitrogenous  aliment.  The  true 
and  only  ferment  of  vinegar  is  the  little  fungus;  it 
is  the  great  agent  of  the  phenomenon;  it,  indeed, 
accomplishes  all. 

Is  there  not  a  great  charm  in  seeing  an  obscure 
subject  clearly  illuminated  by  facts  well  understood 
and  well  interpreted  ?  If  in  a  bottle  containing  wine 
and  air  and  raised  to  a  temperature  of  50°  or  60° 
the  wine  never  turns  sour,  it  is  because  the  germs 
of  the  mycoderma  aceti,  which  the  wine  and  the 
air  hold  in  suspension,  are  deprived  of  all  vitality 
by  the  heat.  Placed,  however,  in  contact  with  ordi- 
nary air,  this  once-heated  wine  can  turn  sour ;  because, 
though  the  germs  of  the  mycoderma  aceti  contained 
at  first  in  the  wine  are  killed,  this  is  not  the  case 
with  those  derived  from  the  surrounding  air.  Pure 
alcoholised  water  never  turns  sour,  even  in  contact 
with  ordinary  air,  and  with  whatever  germs  this  air 
may  carry,  or  that  may  be  found  in  the  dust  of  the 
vessels  which  receive  it.  The  reason  is  that  these 


ACETIC  FEKMENTATTON.  73 

germs  cannot  become  fertile  because  of  the  absence  of 
their  indispensable  food.  Wine  in  bottles  well  filled 
and  laid  flat  do  not  acetify ;  this  is  because  the  myco- 
derm  cannot  multiply  for  lack  of  oxygen.  Without 
doubt  the  air  constantly  penetrates  through  the  pores 
of  the  cork,  but  always  in  such  feeble  quantities  that 
the  colouring  matters  of  the  wine,  and  other  more  or 
less  oxydisable  constituents,  take  possession  of  it  with- 
out leaving  the  smallest  quantity  for  the  germs  of  the 
mycoderm  which  are  generally  suspended  in  the 
wine.  When  the  bottle  is  upright  the  conditions  are 
quite  altered.  The  desiccation  of  the  cork  renders  it 
much  more  permeable  to  the  air,  and  the  germs  of 
the  mycoderm  on  the  surface  of  the  liquid,  if  any 
exist  there,  are  enveloped  by  air. 

Thus,  to  recapitulate  in  a  few  words  the  principles 
which  have  just  been  established  ;  it  is  easy  to  see  that 
the  formation  of  vinegar  is  always  preceded  by  the  de- 
velopment, on  the  surface  of  the  wine,  of  a  little  plant 
formed  of  strangulated  particles,  of  an  extreme  tenuity, 
and  the  accumulation  of  which  sometimes  takes  the 
form  of  a  hardly  visible  veil,  sometimes  of  a  wrinkled 
film  of  very  slight  thickness,  and  greasy  to  the  touch, 
because  of  the  various  fatty  matters  which  the  plant 
contains. 

This  cryptogam  has  the  singular  property  of  con- 
densing considerable  quantities  of  oxygen  and  of  pro- 
voking the  fixa  tion  of  this  gas  upon  the  alcohol,  which 


74  LOUIS  PASTEUR. 

.is  thereby  transformed  into  acetic  acid.  The  little 
mycoderm  is  not  less  exacting  than  larger  vegetables. 
It  must  have  its  appropriate  aliments.  Wine  offers 
them  in  abundance  :  nitrogenous  matters,  the  phos- 
phates of  magnesia  and  of  potash.  The  mycoderm 
thrives,  moreover,  in  warm  climates.  To  cultivate 
it  in  temperate  regions  like  ours  it  is  well  to  warm 
artificially  the  places  where  it  is  cultivated.  But  if 
wine  contains  within  itself  all  the  elements  necessary 
to  the  life  of  the  little  mycoderm,  this  life  is  further 
promoted  by  rendering  the  wine  more  acid  through 
the  addition  of  acetic  acid. 

What,  then,  can  be  more  simple  than  to  produce 
vinegar  from  wine — a  manufacture  which  justly  makes 
the  reputation  of  the  town  of  Orleans  ?  Take  some 
wine,  and  after  having  mixed  with  it  one-fourth  or 
one-third  of  its  volume  of  vinegar  already  formed, 
sow  on  its  surface  the  little  plant  which  does  the  work 
of  acetification.  It  is  only  necessary  to  skim  off,  by 
means  of  a  wooden  spatula,  a  little  of  the  mycodermic 
film  from  a  liquid  covered  with  it,  and  to  transfer  it 
to  the  liquid  to  be  acetified.  The  fatty  matters  which 
it  contains  render  the  wetting  of  it  difficult.  Thus, 
when  we  plunge  into  the  liquid  the  spatula  covered 
with  the  film,  the  latter  detaches  itself  and  spreads 
out  over  the  surface  instead  of  falling  to  the  bottom. 
When  we  operate  in  summer,  or  in  a  room  heated  to 
15°  or  25°  Centigrade  in  winter,  in  twenty-four  or 


ACETIC  FERMENTATION.  75 

forty-eight  hours  at  most,  the  mycoderm  covers  the 
whole  liquid,  so  easy  and  rapid  is  its  development. 
After  some  days  all  the  wine  has  become  vinegar. 

On  one  occasion,  in  a  discussion  which  he  was  hold- 
ing at  the  Academy  of  Sciences,  Pasteur,  wishing  to 
affirm  the  prodigious  activity  of  the  life  and  multipli- 
cation of  this  little  organism,  expressed  himself  thus  :— 

'  I  would  undertake  in  the  space  of  twenty-four 
hours  to  cover  with  mycoderma  aceti  a  surface  of 
vinous  liquid  as  large  as  the  hall  in  which  we  are 
here  assembled.  I  should  only  have  to  sow  in  it  the 
day  before  almost  invisible  particles  of  newly-formed 
mycoderma  aceti.' 

Let  the  reader  try  to  imagine  the  millions  upon 
millions  of  little  mycoderma  particles  which  would 
come  to  life  in  that  one  day. 

But  how  is  the  mycoderm  seed  to  be  obtained  in  the 
first  instance  ?  Nothing  more  simple.  The  mycoderma 
aceti  is  one  of  those  little  so-called  '  spontaneous  '  pro- 
ductions which  are  sure  to  appear  of  themselves  on  the 
surface  of  liquids  or  infusions  suitable  to  their  develop- 
ment. In  wine,  in  vinegar,  or  suspended  in  air,  every- 
where around  us,  in  our  towns,  in  our  houses,  there 
exist  germs  of  this  little  plant.  If  we  wish  to  procure 
some  fresh  mycoderm  it  is  only  necessary  to  put  a 
mixture  of  wine  and  vinegar  into  a  wrarm  place.  In 
a  few  days,  generally,  if  not  always,  there  appear  here 
and  there  little  greyish  patches  scattering  the  light 


76  LOUIS  PASTEUR. 

instead  of  regularly  reflecting  it,  as  does  the  surround- 
ing liquid.  These  specks  go  on  increasing  progres- 
sively and  rapidly.  This  is  the  mycoderma  aceti 
raised  from  the  seeds  which  the  wine  or  the  added 
vinegar  contained,  or  which  the  air  deposited ;  just  as 
we  see  a  field  covered  with  divers  weeds  by  seeds  natu- 
rally distributed  in  the  earth,  or  which  have  been 
brought  to  it  by  the  wind  or  by  animals.  Even  in 
this  last  circumstance  the  comparison  holds  good,  for 
after  you  have  put  wine  or  vinegar  in  a  warm  place 
there  soon  appear,  whence  we  know  not,  little  reddish 
flies,  so  commonly  seen  in  vinegar  manufactories,  and 
in  all  places  where  vegetable  matter  is  turning  sour. 
With  their  feet,  or  with  their  probosces,  these  flies 
transport  the  seed. 

At  Orleans  the  process  for  the  manufacture  of 
vinegar  is  very  simple.  Barrels  ranged  over  each 
other  have  on  each  of  their  vertically-placed  bottoms 
a  circular  opening  some  centimeters  in  diameter,  and 
a  smaller  hole  adjacent,  called  fausset,  for  the  air  to 
pass  in  and  out  when  the  large  opening  is  closed, 
either  by  the  funnel,  through  which  the  wine  is  intro- 
duced, or  by  the  syphon,  which  is  used  for  draw- 
ing off  the  vinegar.  These  barrels,  of  which  the 
capacity  is  230  litres,  are  half  filled.  The  manual 
labour  consists  in  keeping  up  a  suitable  temperature 
in  the  vessel,  and  in  drawing  from  it  every  eight  days 


ACETIC   FERMENTATION.  77 

about  eight  or  ten  litres  of  vinegar,  which  are  replaced 
by  eight  or  ten  litres  of  wine. 

A  barrel  in  which  this  give-and-take  of  wine  and 
vinegar  goes  on  is  technically  called  a  '  mother.'  The 
starting  of  a  'mother'  is  not  a  rapid  process.  We 
begin  by  introducing  into  the  barrel  100  litres  of  very 
good  and  very  limpid  vinegar ;  then  two  litres  only  of 
wine  are  added.  Eight  days  after,  three  litres  of  wine 
are  added,  a  week  later  four  or  five,  until  the  barrel 
contains  about  180  to  200  litres.  Then  for  the  first 
time  vinegar  is  drawn  off  in  sufficient  quantity  to 
bring  back  the  volume  of  the  liquid  to  about  100 
litres.  At  this  moment  the  labours  of  the  '  mother  ' 
begin.  Henceforward  ten  litres  of  vinegar  may  be  drawn 
off  every  eight  days,  to  be  replaced  by  ten  litres  of 
wine.  This  is  the  maximum  that  a  cask  can  yield  in 
a  week.  When  the  casks  work  badly,  as  is  often  the 
case,  it  is  necessary  to  diminish  their  production. 

This  Orleans  system  has  many  drawbacks.  It 
requires  three  or  four  months  to  prepare  what  is 
called  a  '  mother,'  which  must  be  nourished  with  wine 
very  regularly  once  a  week  under  penalty  of  seeing  it 
lose  all  its  power.  Then  it  is  necessary  to  continue 
the  manufacture  at  all  times,  whether  the  vinegar 
be  required  or  not.  To  reconstitute  a  '  mother,'  one 
must  begin  from  the  very  beginning,  a  process  which 
involves  a  loss  of  three  or  four  months'  time.  Lastly 
— a  condition  which  is  at  times  very  inconvenient 


78  LOUIS  PASTEUK. 

— a  '  mother '  cannot  be  transported  from  one  place  to 
another,  or  even  from  one  part  of  the  same  locality  to 
another.  The  'mother,'  in  fact,  must  rest  immovable. 

Pasteur  advised  the  suppression  of  the  '  mothers.' 
He  recommended  an  apparatus,  which  is  simply 
a  vat,  placed  in  a  chamber  the  temperature  of  which 
can  be  raised  to  20°  or  25°  Centigrade.  In  these 
vats  vinegar  already  formed  is  mixed  with  wine.  On 
the  surface  is  sown  the  little  plant  which  converts 
the  wine  into  vinegar.  The  mode  of  sowing  it  has 
been  already  explained.  The  acetification  begins  with 
the  development  of  the  plant. 

A  great  merchant  of  Orleans,  who  had  from  the 
first  adopted  Pasteur's  process,  and  who  had  won  the 
prize  offered  by  the  '  Society  for  the  Encouragement 
of  National  Industry'  for  a  manufactory  perfected 
after  these  principles,  has  stated  that  at  the  end 
of  nine  or  ten  days,  sometimes  even  in  eight,  all 
the  acetified  wine  is  converted 'into  vinegar.  From  a 
hundred  litres  of  wine  he  drew  off  ninety-five  litres  of 
vinegar.  After  the  great  rise  of  temperature  observed 
at  the  moment  of  the  formation  of  the  vinegar,  and 
which  is  caused  by  the  chemical  union  of  the  alcohol 
and  the  oxygen  of  the  air,  the  vinegar  is  allowed  to 
cool.  It  may  then  be  drawn  from  the  vat,  introduced 
into  barrels,  refined,  and  straightway  delivered,  fit  for 
consumption.  When  the  vat  is  quite  emptied,  and  well 
cleaned,  a  new  mixture  is  made  of  vinegar  and  wine, 


ACETIC  FERMENTATION.  79 

the  little  plant  is  sown  as  before,  and  the  same  facts 
are  reproduced  in  the  second  as  in  the  first  operation. 

In  the  vessels  where  vinegar  is  preserved,  whether 
in  the  manufactories,  in  private  houses,  or  in  grocers' 
shops,  it  often  happens  that  the  liquid  becomes  turbid, 
and  impoverished  in  an  extraordinary  manner ;  it  even 
ends  in  putrefaction,  if  a  remedy  be  not  promptly 
applied.  Pasteur  has  pointed  out  the  cause  of  these 
phenomena.  After  the  alcohol  has  become  acetic  acid 
by  the  combustive  action  of  the  mycoderm,  the  ques- 
tion remains,  what  becomes  of  the  mycoderm  ?  Most 
frequently  it  falls  to  the  bottom  of  the  vessel,  having 
no  more  work  to  accomplish.  This  is  a  phase  of  the 
manufacture  which  must  be  watched  with  care.  It 
is  shown  by  the  experiments  of  Pasteur  that  the 
mycoderma  aceti  can  live  on  vinegar  already  formed, 
maintaining  its  power  of  fixing  the  oxygen  on  certain 
constituents  of  the  liquid.  In  this  case  the  acetic 
acid  itself  is  the  seat  of  the  chemical  action— in  other 
wrords,  the  oxygen  unites  with  the  carbon  of  the 
acetic  acid,  and  transforms  it  into  carbonic  acid,  and 
as  the  acetic  acid  has  a  composition  which  can  be 
represented  by  carbon  and  water,  it  follows  that  if 
the  combustion  is  allowed  to  take  its  course,  instead 
of  vinegar  we  have  eventually  nothing  but  water 
mixed  with  a  small  proportion  of  nitrogenous  and 
mineral  matters,  and  the  remains  of  the  mycoderm. 


80  LOUIS  PASTEUR. 

We  have  thus  an  ordinary  organic  infusion  exempt 
from  all  acidity,  and  one  which  could  not  be  better 
fitted  to  become  the  prey  of  the  vibrios  of  putrefaction 
or  of  the  aerobic  mucors.  By  these  mucors,  more- 
over, which  form  a  film  on  the  surface  of  the  liquid 
after  the  mycoderm  has  fallen,  the  anaerobic  vibrios, 
protected  from  the  action  of  the  air,  can  come  into 
active  existence.  Here  we  find  ourselves  in  presence 
of  one  of  those  double  phenomena,  of  putrefaction  in 
the  deeper  parts  of  the  liquid,  and  of  combustion  at 
the  surface  which  is  in  contact  with  the  air.  Nothing 
is  more  prejudicial  to  the  quality  of  the  vinegar  than 
the  setting  in  of  this  combustion  after  the  vinegar  has 
been  formed,  and  when  it  contains  no  more  alcohol. 
The  first  materials  of  the  vinegar  upon  which  the 
oxygen  transmitted  by  the  mycoderm  fixes  are,  in  fact, 
the  ethereal  and  aromatic  constituents  which  give  to 
vinegar  its  chief  value. 

Another  cause  of  the  deterioration  of  the  quality 
of  vinegar,  which  is  sometimes  very  annoying  to  the 
manufacturer,  consists  in  the  frequent  presence  of 
little  eel-like  organisms,  very  curious  when  viewed 
with  a  strong  magnifier.  Their  bodies  are  so  trans- 
parent that  their  internal  organs  can  be  easily  dis- 
tinguished. These  eel-like  creatures  multiply  with  ex- 
traordinary rapidity.  Certainly  there  is  not  a  single 
barrel  of  vinegar  manufactured  by  the  Orleans  system 
which  does  not  contain  them  in  alarming  numbers. 


ACETIC  FEKMENTATTON.  81 

Prior  to  Pasteur's  investigations,  the  ignorance  re- 
garding these  organisms  was  such  that  they  were 
actually  considered  necessary  to  the  production  of  the 
vinegar ;  whereas  they  are,  on  the  contrary,  most  inimi- 
cal to  it,  and  must,  if  possible,  be  got  rid  of.  This  is, 
moreover,  rendered  desirable  by  the  repugnance  which 
is  naturally  felt  to  using  a  liquid  denied  by  the  presence 
of  such  animalcules — a  repugnance  which  becomes 
almost  insurmountable  to  anyone  who  has  once  seen 
through  a  microscope  the  swarms  contained  in  a  drop 
of  vinegar.  The  mischief  wrought  by  these  little 
beings  in  the  manufacture  of  vinegar  results  from  the 
fact  that  they  require  air  to  live.  The  effect  can 
easily  be  perceived  by  tilling  to  the  brim  a  bottle  of 
vinegar,  corking  it,  and  then  comparing  it  with  a 
similar  bottle  half  filled  with  the  same  vinegar,  and  left 
uncorked  in  contact  with  the  air.  In  the  first  bottle, 
the  motions  of  the  eel-like  creatures  become  gradually 
slower,  until  after  a  few  days  they  cease  to  multiply 
and  fall  lifeless  to  the  bottom  of  the  vessel.  In  the 
second  bottle,  on  the  contrary,  they  continue  to  swarm 
and  move  about.  This  need  of  oxygen  is  further  de- 
monstrated by  the  fact  that,  if  the  vinegar  reaches  a 
certain  depth  in  the  bottle,  life  is  suspended  in  the 
lower  parts,  and  the  little  eel-like  organisms,  in  order 
to  breathe  more  freely,  form  a  crawling  zone  in  the 
upper  layers  of  the  liquid. 

Connecting  these  observations  with  the  other  fact 


82  LOUIS  PASTEUR. 

that  the  vinegar  is  formed  by  the  action  of  the  myco- 
dermic  film  on  its  surface,  we  can  understand  at  once 
that  the  mycoderm  and  the  little  eels  continually 
carry  on  a  struggle  for  existence,  since  both  of  these 
living  things — the  one  animal  the  other  vegetable — 
imperiously  demand  the  same  aliment,  oxygen.  They 
live,  moreover,  in  the  same  superficial  layers,  a  circum- 
stance which  gives  rise  to  very  curious  phenomena. 
When,  for  one  reason  or  another,  the  film  of  myco- 
derm is  not  formed,  or  when  there  is  any  delay  in 
its  production,  the  little  eels  invade  in  such  great 
numbers  the  upper  layers  of  the  liquid  that  they 
absorb  all  the  oxygen.  The  little  plant  has  in  conse- 
quence great  difficulty  in  developing  itself  or  even  in 
beginning  its  life.  Reciprocally,  when  the  work  of 
acetification  is  active,  and  when  the  mycoderm  has 
occupied  the  upper  layers,  it  gradually  drives  away 
the  eels,  which  take  refuge,  not  deep  down,  where 
they  would  perish,  but  against  the  moist  sides  of  the 
barrel  or  the  vat.  There  they  form  a  thick  whitish 
scum  all  in  motion.  It  is  a  very  curious  spectacle. 
Here  their  enemy,  the  mycoderm,  can  no  longer 
injure  them  to  the  same  extent,  since  they  are  sur- 
rounded with  air ;  and  here  they  wait  with  impatience 
for  the  moment  when  they  can  again  take  their  place 
in  the  liquid,  and,  in  their  turn,  fight  against  the 
mycoderm.  In  Pasteur's  process,  where  the  vats  are 
very  often  cleansed,  it  is  easy  to  keep  them  free  from 


ACETIC   FERMENTATION.  83 

these  little  animalcules ;  they  have  not  time  to  multiply 
to  a  hurtful  extent.  Indeed,  if  the  operation  be  well 
conducted,  they  do  not  make  their  appearance  at  all. 

Nearly  all  Pasteur's  publications  have  had  from 
the  moment  of  their  appearance  to  undergo  the  severest 
criticism.  Their  novelty  caused  them  to  clash  with 
the  prejudices  and  errors  current  in  science.  His  re- 
searches on  fermentation  provoked  lively  opposition. 
Liebig  did  not  accept  without  recrimination  a  series 
of  researches  which  concurred  in  upsetting  the  theory 
he  had  enunciated  and  defended  in  all  his  works. 
After  having  kept  silence  for  ten  years,  he  published, 
at  Munich,  where  he  was  professor,  a  long  memoir 
entirely  directed  against  Pasteur's  results.  In  1870, 
on  the  eve  of  the  war,  Pasteur,  who  was  at  that  time 
returning  from  a  scientific  journey  into  Austria,  deter- 
mined to  pass  by  Munich,  with  the  view  of  attempting 
to  convince  his  distinguished  adversary.  Liebig  re- 
ceived him  with  great  courtesy,  but,  hardly  recovered 
from  an  illness,  he  alleged  his  convalescence  as  a 
reason  for  declining  all  discussion. 

Then  followed  the  Franco-German  war.  Hardly 
was  it  terminated  when  Pasteur  brought  before  the 
Academy  of  Sciences  a,t  Paris  a  defence  of  what  he 
had  published,  as  a  sort  of  challenge  to  his  illustrious 
opponent.  The  memoir  of  Liebig  was  filled  with  the 
most  skilful  arguments. 


84  LOUIS  PASTEUR. 

'  I  pondered  it  for  nearly  ten  years  before  producing 
it,'  he  wrote.  Pasteur,  putting  aside  all  subtleties  of 
argument,  went  straight  to  the  two  objections  of  the 
German  chemist  which  lay  at  the  root  of  the  discussion. 

It  may  be  remembered  that  one  of  the  most  de- 
cisive proofs  by  which  Pasteur  overthrew  Liebig's 
theory  resulted  from  the  experiments  in  which  by 
the  aid  of  mineral  bodies  and  fermentable  matter  he 
produced  a  special  living  ferment  for  each  definite  fer- 
mentation. By  removing  all  nitrogenous  organic 
matter,  which  in  Liebig's  theory  constitutes  the  fer- 
ment, Pasteur  established,  at  one  and  the  same  time, 
the  life  of  the  ferment  and  the  absence  of  all  action  of 
albuminoid  matter  in  process  of  alteration.  Liebig 
here  formally  contested  the  fact  that  Pasteur  had  been 
able  to  produce  yeast  and  alcoholic  fermentation  in  a 
sweetened  mineral  medium  by  sowing  therein  an  in- 
finitesimal quantity  of  yeast.  It  is  certain  that,  ten 
years  previously,  when  Pasteur  announced  the  pro- 
duction of  yeast  life  and  alcoholic  fermentation  under 
such  conditions,  his  experiment  was  one  so  difficult  to 
perform  that  it  sometimes  happened  to  Pasteur  him- 
self to  be  unable  to  reproduce  it.  The  cells  of  yeast 
sown  in  the  sweetened  mineral  medium  found  them- 
selves often  associated  with  other  microscopic  or- 
ganisms, which  were  singularly  hurtful  to  the  life  of 
the  yeast.  Pasteur  was  at  this  period  far  from  being 
familiarised  with  the  delicacy  which  such  experiments 


ACETIC  FERMENTATION.  85 

require,  and  he  did  not  yet  know  all  the  precau- 
tions indicated  later  on,  which  were  indispensable  to 
success.  Though  in  his  original  memoir  of  1860 
Pasteur  had  pointed  out  the  difficulties  of  his  experi- 
ment, these  difficulties  existed  nevertheless.  Liebig 
took  hold  of  them  with  skill,  exaggerated  them ;  saw, 
so  to  speak,  nothing  but  them ;  and  declared  that  the 
results  announced  never  could  have  been  obtained. 
But  in  1871  the  fundamental  experiment  of  Pasteur, 
on  the  life  of  yeast  in  a  sweetened  mineral  medium, 
had  become  a  trifle  for  him.  He  knew  exactly  how 
to  form  media  deprived  of  all  foreign  germs,  how  to 
prepare  pure  yeast,  and  how  to  prevent  the  introduc- 
tion of  new  germs,  which  could  develop  in  the  liquids 
and  hinder  the  life  of  the  yeast. 

'  Choose,'  said  he  to  Liebig,  '  from  the  members 
of  the  Academy  one  or  several,  and  ask  them  to  de- 
cide between  you  and  me.  I  am  ready  to  prepare 
before  you  and  before  them,  in  a  sweetened  mineral 
medium,  as  much  yeast  as  you  can  reasonably  ask  for, 
and  with  substances  provided  by  yourself.' 

Liebig's  second  objection  had  reference  to  acetic 
fermentation.  The  process  of  acetification  known  as 
that  of '  beech  shavings '  is  widely  practised  in  Germany 
and  even  in  France.  It  consists  in  causing  alcohol 
diluted  with  water  and  with  the  addition  of  some 
milliemes  of  acetic  acid  to  trickle  slowly  into  barrels 
or  vats  filled  with  shavings  of  beech,  either  massed 


86  LOUIS  PASTEUE. 

together  without  order  or  disposed  in  layers  after  hav- 
ing been  rolled  up  like  the  spring  of  a  watch.  Openings 
formed  in  the  sides  of  the  barrel,  and  in  a  double 
bottom  upon  which  the  shavings  rest,  permit  the 
access  of  the  air,  which  rises  into  the  barrel  as  it 
would  in  a  chimney,  and  yields  all  or  part  of  its 
oxygen  to  the  alcohol  to  convert  it  into  acetic  acid. 
All  writers  prior  to  Pasteur,  and  Liebig  in  particular, 
maintained  that  the  shavings  acted  like  porous  bodies 
in  the  same  manner  as  finely  divided  platinum.  The 
acetic  acid,  they  said,  was  formed  by  a  direct  oxidation, 
without  any  other  influence  than  the  porosity  of  the 
wood.  This  view  of  the  subject  was  rendered  plausible 
by  the  fact  that  in  many  manufactories  the  alcohol 
employed  is  that  of  distillation,  which  contains  no  al- 
buminoid substances.  Moreover,  the  duration  of  the 
shavings  is  in  a  sense  indefinite. 

According  to  Pasteur,  the  shavings  perform  only  a 
passive  part  in  the  manufacture.  They  promote  the 
division  of  the  liquid  and  cause  a  considerable  aug- 
mentation of  the  surface  exposed  to  the  air.  They 
moreover  serve  as  a  support  for  the  ferment,  which  is 
still,  according  to  him,  the  mycoderma  aceti,  under  the 
mucous  form  proper  to  it  when  submerged. 

Certainly  appearances  were  far  from  being  favour- 
able to  this  view.  When  the  shavings  of  a  barrel 
which  has  been  in  work  for  several  months  or  even  for 
several  years  are  examined,  they  are  found  to  be  extra- 


ACETIC   FEKMENTATION.  87 

ordinarily  clean.  It  might  be  said  that  they  had  just 
been  carefully  washed.  Pasteur  has  shown  that  this 
is  but  a  deceptive  appearance,  and  that  in  reality 
these  shavings  are  partly  or  wholly  covered  with  a 
mucous  film  of  mycoderma  aceti  of  excessive  tenuity. 
It  is  necessary  to  scrape  the  surface  of  the  wood  with  a 
scalpel  and  examine  the  scrapings  with  the  microscope 
to  be  assured  of  the  presence  of  this  pellicle. 

Liebig,  who  somewhere  speaks,  not  without  a  cer- 
tain contempt,  of  the  microscope,  denied  formally  the 
exactitude  of  these  assertions. 

'  With  diluted  alcohol,  which  is  used  for  the  rapid 
manufacture  of  vinegar,'  he  wrote,  '  the  elements  of 
nutrition  of  the  mycoderm  are  excluded,  and  the 
vinegar  is  made  without  its  intervention.'  He  asserted 
also  in  his  memoir  of  1869  that  he  had  consulted  the 
head  of  one  of  the  principal  manufactories  of  vinegar 
in  Germany,  that  in  this  manufactory  the  diluted  al- 
cohol did  not  receive  during  the  whole  course  of  its  trans- 
formation any  foreign  addition,  and  that  beyond  the  air 
and  the  surfaces  of  wood  and  charcoal — for  charcoal  is 
sometimes  associated  with  the  beech  shavings — nothing 
can  act  upon  the  alcohol.  Liebig  added  that  the 
director  of  the  manufactory  did  not  believe  at  all  in 
the  presence  of  the  mycoderm,  and  that  finally  he, 
Liebig,  in  examining  the  shavings  which  had  been 
used  for  twenty-five  years  in  the  manufactory,  saw  no 
trace  of  mycoderm  on  their  surface. 


88  LOUIS  PASTEUR. 

The  argument  appeared  conclusive.  How,  in  fact, 
could  we  understand  the  production  of  a  plant  con- 
taining within  itself  nitrogen  and  mineral  elements 
which  was  nevertheless  to  be  nourished  by  water  and 
alcohol. 

'  You  do  not  take  into  account,'  replied  Pasteur, 
'  the  nature  of  the  water  which  serves  to  dilute  your 
alcohol.  This  water,  like  all  ordinary  waters,  even 
the  purest,  contains  salts  of  ammonia  and  mineral 
matters  which  are  capable  of  nourishing  the  plant. 
Finally,  you  have  not  rightly  examined  with  the  micro- 
scope the  surface  of  the  shavings,  otherwise  you  would 
have  seen  the  little  particles  of  the  mycoderma  aceti 
united,  in  some  cases,  to  a  thin  film  which  can  even  be 
lifted  up.  I  propose  to  you,  moreover,  to  send  to  the 
Academic  Commission  charged  with  the  decision  of  the 
debate,  some  shavings  that  you  have  obtained  yourself 
in  the  manufactory  at  Munich,  and  in  the  presence  of 
its  director.  I  will  undertake  to  prove  before  the  mem- 
bers of  the  commission  the  presence  of  the  mycoderm 
on  the  surface  of  these  shavings.' 

Liebig  did  not  accept  this  challenge.  To-day  the 
question  is  decided. 


THE  QUESTION  OF  SPONTANEOUS 
GENERATION. 

'  ALL  dry  bodies,'  said  Aristotle, '  which  become  damp, 
and  all  damp  bodies  which  are  dried,  engender  animal 
life.'  Bees,  according  to  Virgil,  are  produced  from 
the  corrupted  entrails  of  a  young  bull.  At  the  time 
of  Louis  XIV.  we  were  hardly  more  advanced.  A 
celebrated  alchemist  doctor,  Van  Helmont,  wrote : 
'  The  smells  which  rise  from  the  bottom  of  morasses 
produce  frogs,  slugs,  leeches,  grasses,  and  other 
things.'  But  most  extraordinary  of  all  was  the  true 
recipe  given  by  Van  Helmont  for  producing  a  pot 
of  mice.  It  suffices  to  press  a  dirty  shirt  into  the 
orifice  of  a  vessel  containing  a  little  corn.  After  about 
twenty-one  days,  the  ferment  proceeding  from  the  dirty 
shirt  modified  by  the  odour  of  the  corn  effects  the  trans- 
mutation of  the  wheat  into  mice.  Van  Helmont,  who 
asserted  that  he  had  witnessed  the  fact,  added  with 
assurance : 

'  The  mice  are  born  full  grown ;  there  are   both 


90  LOUIS  PASTEUE. 

males   and   females.      To    reproduce   the   species   it 
suffices  to  pair  them.' 

'  Scoop  out  a  hole,'  said  he  again,  '  in  a  brick,  put 
into  it  some  sweet  basil,  crushed,  lay  a  second  brick 
upon  the  first  so  that  the  hole  may  be  perfectly 
covered.  Expose  the  two  bricks  to  the  sun,  and  at 
the  end  of  a  few  days  the  smell  of  the  sweet  basil, 
acting  as  a  ferment,  will  change  the  herb  into  real 
scorpions.  An  Italian  naturalist,  Eedi,  was  the  first 
to  subject  this  question  of  spontaneous  generation 
to  a  more  attentive  examination.  He  showed  that 
maggots  in  meat  are  not  spontaneously  generated, 
but  that  they  are  the  larvse  of  flies'  eggs.  To  prevent 
the  production  of  maggots,  Redi  showed  that  it  was 
only  necessary  to  surround  the  meat  with  fine  gauze 
before  exposing  it  to  the  air.  As  no  flies  could  alight 
upon  meat  thus  protected,  there  were  no  eggs  de- 
posited, and  consequently  neither  larvse  nor  maggots. 
But  at  the  moment  when  the  doctrine  of  spontaneous 
generation  began  to  lose  ground  by  the  limitation  of 
its  domain,  the  discovery  of  the  microscope  brought 
to  this  doctrine  new  and  formidable  support.  In  pre- 
sence of  the  world  of  animalculae,  the  partisans  of 
spontaneous  generation  raised  a  note  of  triumph. 
'  We  may  have  been  mistaken,'  they  said,  '  as  to  the 
origin  of  mice  and  maggots,  but  is  it  possible  to 
believe  that  microscopic  organisms  are  not  the  out- 
come of  spontaneous  generation  ?  How  can  we  other- 


THE  QUESTION   OF  SPONTANEOUS   GENERATION.       91 

wise  explain  their  presence  and  rapid  multiplication 
in  all  dead  animal  or  vegetable  matter  in  process  of 
decomposition  ? ' 

Buffon  lent  the  authority  of  his  name  to  the  doc- 
trine of  spontaneous  generation.  He  even  devised 
a  system  to  explain  this  hypothesis.  In  1745  two 
ecclesiastics  entered  upon  an  eager  controversy  for 
and  against  this  question.  While  the  English  Catholic 
priest  Needham  adopted  the  theory  of  spontaneous 
generation,  the  Italian  priest  Spallanzani  energetically 
opposed  it ;  but  while  in  the  eyes  of  the  public  the 
Italian  remained  master  of  the  dispute,  his  success  was 
more  apparent  than  real,  more  in  word  than  in  deed. 

The  problem  was  again  brought  forward  in  a  more 
emphatic  manner  in  1858.  M.  Pouchet,  director  of 
the  Museum  of  Natural  History  at  Rouen,  in  address- 
ing the  Academy  of  Sciences,  declared  that  he  had 
succeeded  in  demonstrating  in  a  manner  absolutely 
certain  the  existence  of  microscopic  living  organisms, 
which  had  come  into  the  world  without  germs,  and 
consequently  without  parents  similar  to  themselves. 

How  came  Pasteur  to  throw  himself  into  this  dis- 
cussion, at  first  sight  so  far  removed  from  his  other 
occupations  ?  The  results  of  his  researches  on  fer- 
mentation led  him  to  it  as  a  sort  of  duty.  He  was 
carried  on  by  a  series  of  logical  deductions.  Let  us 
recall  to  mind,  for  example,  the  experiment  in  which 
Pasteur  exposed  to  the  heat  of  the  sun  water  sweetened 


92  LOUIS  PASTEUR. 

with  sugar  and  mixed  with  phosphates  of  potash  and 
magnesia,  a  little  sulphate  of  ammonia,  and  some  car- 
bonate of  lime.  In  these  conditions  the  lactic  fermen- 
tation was  often  seen  to  develop  itself — that  is  to  say, 
the  sugar  became  lactic  acid,  which  combined  with  the 
lime  of  the  carbonate  to  form  lactate  of  lime.  This 
salt  crystallises  in  long  needles,  and  ends  sometimes  by 
filling  the  whole  vase,  while  a  little  organised  living 
thing  is  at  the  same  time  produced  and  multiplied.  If 
the  experiment  is  carried  on  further,  another  fermenta- 
tion generally  succeeds  to  this  one.  Moving  vibrios 
make  their  appearance  and  multiply,  the  lactate  of  lime 
disappears,  the  fluidity  returns  to  the  mass,  and  the 
lactate  finds  itself  replaced  by  butyrate  of  lime.  What 
a  succession  of  strange  phenomena  !  How  did  life 
appear  in  this  sweetened  medium,  composed  originally 
of  such  simple  elements,  and  apparently  so  far  re- 
moved from  all  production  of  life?  This  lactic  fer- 
ment, these  butyric  vibrios,  whence  do  they  come  ? 
Are  they  formed  of  themselves  ?  or  are  they  produced 
by  germs  ?  If  the  latter,  whence  do  the  germs  come  ? 
The  appearance  of  living  organised  ferments  had  be- 
come for  Pasteur  the  all-important  question,  since  in 
all  fermentations  he  had  observed  a  correlation  between 
the  chemical  action  set  up  and  the  presence  of  micro- 
scopic organisms.  Prior  to  the  establishment  of  the 
facts  already  mentioned,  these  difficulties  did  not  exist. 
The  theory  of  Liebig  was  universally  accepted. 


THE  QUESTION    OF  SPONTANEOUS   GENERATION.       93 

Thus  the  question  as  to  the  origin  of  microscopic 
organisms  and  the  part  played  by  them  in  fermenta- 
tion was  imposed  as  a  necessity  on  Pasteur.  He 
could  not  proceed  further  in  his  researches  without 
having  solved  this  question. 

In  the  month  of  October,  1857,  Pasteur  was  called 
to  Paris.  After  having  been  made  dean  at  an  incredibly 
early  age,  he  was  now,  at  the  age  of  thirty-five,  entrusted 
with  the  scientific  studies  at  the  Ecole  Normale 
Superieure.  But  if  the  position  was  flattering,  it  did  not 
give  to  Pasteur  what  he  most  desired.  As  he  had  no 
Professor's  chair,  he  had  no  laboratory.  In  those  days 
science,  and  the  higher  education  in  science,  were  at  a 
discount.  It  was  the  period  when  Claude  Bernard 
lived  in  a  small  damp  laboratory,  when  M.  Berthelot, 
though  known  through  his  great  labours,  was  still 
nothing  more  than  an  assistant  in  the  College  de 
France. 

At  the  time  here  referred  to,  the  Minister  of  Public 
Instruction  said  to  Pasteur,  '  There  is  no  clause  in 
the  budget  to  grant  you  1,500  francs  a  year  to  defray 
the  expense  of  experiments.'  Pasteur  did  not  hesitate 
to  establish  a  laboratory  at  his  own  expense  in  one  of 
the  garrets  of  the  Ecole  Normale.  We  can  readily  ima- 
gine the  modesty  of  such  an  establishment  in  such  a 
place.  Dividing  his  time  between  his  professional 
duties  and  his  laboratory  experiments,  Pasteur  never 
went  out  but  to  talk  over  his  daily  researches  with 


94  LOUIS  PASTEUR. 

M.  Biot,  M.  Dumas,  M.  de  Senarmont,  and  M.  Balard. 
M.  Biot  especially  was  his  habitual  confidant.  The 
day  when  M.  Biot  learned  that  Pasteur  proposed  to 
study  the  obscure  question  of  spontaneous  generation, 
he  strongly  dissuaded  him  from  entangling  himself  in 
this  labyrinth.  '  You  will  never  escape  from  it,'  said 
he,  '  you  will  only  lose  your  time ; '  and  when  Pasteur 
attempted  some  timid  observations  with  the  view  of 
showing  that  in  the  order  of  his  studies  it  was  in- 
dispensable for  him  to  attack  this  problem,  M.  Biot 
grew  angry.  Although  endowed,  as  Sainte-Beuve  has 
said,  with  all  the  qualities  of  curiosity,  of  subtlety,  of 
penetration,  of  ingenious  exactitude,  of  method,  and 
of  perspicuity,  with  all  the  qualities,  in  short,  essential 
and  secondary,  M.  Biot  treated  the  project  of  Pasteur 
as  a  presumptuous  adventure. 

Bolder  than  M.  Biot,  but  with  a  circumspection 
always  alive,  M.  Dumas  declared  to  Pasteur,  without, 
however,  further  insisting  upon  the  point,  that  he 
would  not  advise  anyone  to  occupy  himself  too  long 
with  such  a  subject.  M.  de  Senarmont  alone  took 
the  part  of  Pasteur,  and  said  to  M.  Biot : 

'  Let  Pasteur  alone.  If  there  is  nothing  to  be 
found  in  the  path  which  he  has  entered  upon,  do  not 
be  alarmed,  he  will  not  continue  in  it.  But,'  added 
he,  '  I  should  be  surprised  if  he  found  nothing  in  it.' 

M.  Pouchet  had  previously  stated  the  problem 
with  precision :  . 


THE  QUESTION   OF  SPONTANEOUS  GENERATION.      95 

'  The  opponents  of  spontaneous  generation  assert 
that  the  germs  of  microscopic  organisms  exist  in  the 
air,  which  transports  them  to  a  distance.  What,  then, 
will  these  opponents  say  if  I  succeed  in  inducing  the 
generation  of  living  organisms,  while  substituting 
artificial  air  for  that  of  the  atmosphere  ? ' 

Pouchet  then  devised  this  ingenious  experiment. 
He  filled  a  bottle  with  boiling  water,  hermetically  sealed 
it  with  the  greatest  care,  and  plunged  it  upside  down 
into  a  basin  of  mercury.  When  the  water  was  quite 
cold  he  uncorked  the  bottle  under  the  metal,  and  in- 
troduced into  it  half  a  litre  of  pure  oxygen  gas,  which 
is  as  necessary  to  the  life  of  the  smallest  microscopic 
organism  as  it  is  to  that  of  the  larger  animals  and 
vegetables.  Up  to  this  time  there  was  nothing  in  the 
vessel  but  pure  water  and  oxygen.  Pouchet  then  in- 
troduced a  minute  bunch  of  hay  which  had  been 
enclosed  in  a  corked  bottle,  and  exposed  in  a  stove 
for  a  long  time  to  a  temperature  of  more  than  100 
degrees.  At  the  end  of  eight  days  a  mouldiness 
was  developed  in  this  infusion  of  hay.  '  Where 
does  this  come  from  ?  '  cried  M.  Pouchet  triumphantly. 
Certainly  not  from  the  oxygen,  which  had  been  pre- 
pared from  a  chemical  compound  at  the  temperature 
of  incandescence.  The  water  had  been  equally  deprived 
of  germs,  since  at  the  boiling  temperature  all  germs 
wrould  have  been  destroyed.  The  hay  also  could  not 
have  contained  them,  for  it  had  been  taken  from  a 


96  LOUIS  PASTEUR 

stove  heated  to  100  degrees.  As  it  was  urged,  how- 
ever, that  certain  organisms  could  resist  this  tempera- 
ture, M.  Pouchet  heated  the  hay  from  200  to  300 
degrees,  or  to  any  temperature  that  might  be 
desired. 

Pasteur  came  to  disturb  the  triumph  of  M. 
Pouchet. 

In  a  lecture  which  he  gave  at  the  Sorbonne  in 
1864,  before  a  large  assembly  composed  of  savants, 
philosophers,  ladies,  priests,  and  novelists — Alexandre 
Dumas  was  in  the  first  row — all  showing  eager  interest 
in  the  problems  to  be  dealt  with  in  the  lecture, 
Pasteur  thus  criticised  the  experiment  of  Pouchet : 
'  This  experiment  is  irreproachable,  but  irreproachable 
only  on  those  points  which  have  attracted  the  atten- 
tion of  its  author.  I  will  demonstrate  before  you  that 
there  is  a  cause  of  error  which  M.  Pouchet  has  not 
perceived,  which  he  has  not  in  the  least  suspected, 
which  no  one  before  him  suspected,  but  which 
renders  his  experiment  as  completely  illusory  as 
that  of  Van  Helmont's  pot  of  dirty  linen.  I  will 
show  you  where  the  mice  got  in.  I  will  prove  to 
you,  in  short,  that  it  is  the  mercury  which  carries  the 
germs  into  the  vessels,  or,  rather,  not  to  go  beyond 
the  demonstrated  fact,  the  dust  which  is  suspended  in 
the  air.' 

To  render  visible  this  floating  dust,  Pasteur  caused 
the  hall  to  be  darkened,  and  pierced  the  obscurity  by  a 


THE  QUESTION    OF   SPONTANEOUS   GENERATION.      97 

beam  of  light.  There  then  appeared,  dancing  and  twirl- 
ing in  the  beam,  thousands  of  little  particles  of  dust. 

'  If  we  had  time  to  examine  them  well/  continued 
Pasteur,  '  we  should  see  them,  though  agitated  with 
various  movements,  falling  downwards  more  or  less 
quickly.  It  is  thus  that  all  objects  become  covered 
with  dust — the  furniture,  the  table,  the  mercury  in 
this  basin.  Since  this  mercury  was  taken  from  the 
mine,  how  much  dust  must  have  fallen  upon  it,  to  say 
nothing  of  all  that  has  been  intimately  mixed  up 
with  it  during  the  numerous  manipulations  to  which 
it  has  been  subjected  in  the  laboratory  ?  It  is  not 
possible  to  touch  this  mercury,  to  place  the  hand  in 
it,  or  a  bottle,  without  introducing  into  the  interior  of 
the  basin  the  dust  which  lies  on  its  surface.  You 
will  now  see  what  takes  place.' 

Projecting,  in  the  darkness,  the  beam  of  light  upon 
the  basin  of  mercury,  the  liquid  metal  shone  forth  with 
its  usual  brilliancy.  Pasteur  then  sprinkled  some  dust 
upon  the  mercury,  and,  plunging  a  glass  rod  into  it, 
the  dust  was  seen  to  travel  towards  the  spot  where 
the  rod  entered  the  mercury,  and  to  penetrate  into  the 
space  between  the  glass  and  the  metal. 

'  Yes,'  exclaimed  Pasteur  with  a  voice  which  gave 
evidence  of  the  sincerity  of  his  conviction,  'yes,  M. 
Pouchet  had  removed  the  germs  from  the  water  and 
from  the  hay,  but  he  had  neglected  to  remove  the 
dust  from  the  surface  of  the  mercury.  This  is  the 


98  LOUIS  PASTEUR. 

cause  of  his  error ;  this  is  what  has  vitiated  his  whole 
arrangement.' 

Pasteur  then  instituted  experiments  exactly  similar 
to  those  of  Pouchet,  but  taking  care  to  remove  every 
cause  of  error  which  had  escaped  the  latter.  He  em- 
ployed a  glass  bulb  with  a  long  neck,  which  he  bent, 
and  connected  with  a  tube  of  platinum  placed  in  a 
furnace,  so  that  it  could  be  heated  nearly  to  redness. 
In  the  bulb  he  placed  some  very  putrescible  liquids — 
urine  for  example.  When  the  furnace  which  sur- 
rounded the  platinum  tube  was  in  action,  Pasteur 
boiled  the  liquid  for  some  minutes,  then  he  allowed  it 
to  cool,  keeping  the  fire  around  the  platinum  tube 
still  active.  During  the  cooling  of  the  bulb  the  ex- 
ternal air  was  introduced,  after  having  first  travelled 
through  the  red-hot  platinum  tube.  The  liquid  was 
thus  placed  in  contact  with  air  whose  suspended 
germs  were  all  burnt  up. 

In  an  experiment  thus  carried  out,  the  urine 
remains  unchanged — it  undergoes  only  a  very  slight 
oxidation,  which  darkens  its  colour  a  little — but  it 
exhibits  no  kind  of  putrefaction.  If  it  be  desired  to 
repeat  this  experiment  with  alkaline  liquids,  such  as 
milk,  the  temperature  must  be  raised  a  little  above 
the  boiling  point — a  condition  easily  realised  with  the 
apparatus  just  described.  It  is  only  necessary  to 
connect  with  the  free  extremity  of  the  platinum  tube 
a  glass  tube  bent  at  right  angles,  and  to  plunge  the 
latter  to  a  depth  of  some  centimeters  into  a  basin  of 


THE  QUESTION   OF  SPONTANEOUS   GENERATION.      99 

mercury.  In  these  circumstances  ebullition  goes  on 
under  a  pressure  greater  than  that  of  the  atmo- 
sphere, consequently  at  a  temperature  higher  than 
100  degrees  Centigrade. 

It  remained,  however,  to  be  proved  that  the  floating 
dust  of  the  air  embraces  the  germs  of  the  lower 
organisms.  Through  a  tube  stopped  with  cotton 
wool,  Pasteur,  by  means  of  an  aspirator,  drew  ordi- 
nary air.  In  passing  through  the  wool  it  was  filtered, 
depositing  therein  all  its  dust.  Taking  a  watch-glass, 
Pasteur  placed  on  it  a  drop  of  water  in  which  he 
steeped  the  cotton  wool  stopper  and  squeezed  out  of 
it,  upon  a  glass  slide,  a  drop  of  water  which  contained 
a  portion  of  the  intercepted  dust.  He  repeated  this 
process  until  he  had  extracted  from  the  cotton  nearly 
all  the  intercepted  dust.  The  operation  is  simple  and 
easily  executed.  Placing  the  glass  slide  with  a  little  of 
the  soiled  liquid  under  a  microscope,  we  can  dis- 
tinguish particles  of  soot,  fragments  of  silk,  scraps  of 
wool,  or  of  cotton.  But,  in  the  midst  of  this  inani- 
mate dust,  living  particles  make  their  appearance — 
that  is  to  say,  organisms  belonging  to  the  animal  or 
vegetable  kingdom,  eggs  of  infusoria,  and  spores  of 
cryptogams.  Germs,  animalculae,  flakes  of  mildew, 
float  in  the  atmosphere,  ready  to  fall  into  any  appro- 
priate medium,  and  to  develop  themselves  at  a  pro- 
digious rate. 

But    are    these     apparently    organised    particles 


100  LOUIS  PASTEUR. 

which  are  found  thus  associated  with  amorphous  dust 
indeed  the  germs  of  microscopic  living  beings  ?  Grant- 
ing the  experiment  devised  by  Pasteur  to  verify  that 
of  Pouchet  to  be  irreproachable,  is  Pasteur's  interpre- 
tation of  it  rigorously  true  ?  In  presence  of  the 
problem  of  the  origin  of  life,  all  hypotheses  are  pos- 
sible as  long  as  the  truth  has  not  been  clearly 
revealed.  Truly,  it  might  be  argued,  if  fermenta- 
tion be  caused  by  germs,  then  the  air  which  has 
passed  through  a  red-hot  platinum  tube  cannot  pro- 
voke fermentation,  or  putrefaction,  or  the  formation 
of  organisms,  because  the  germs  of  these  last,  which 
were  suspended  in  the  air,  have  lost  all  vitality.  But 
what  right  have  you  to  speak  of  germs  ?  How  do 
you  know  that  the  previous  existence  of  germs  is 
necessary  to  the  appearance  and  development  of 
microscopic  organisms?  May  not  the  prime  mover 
of  the  life  of  microscopic  organisms  be  some  appro- 
priate medium  started  into  activity  by  magnetism, 
electricity,  or  even  ozone  ?  Now,  by  the  passing  of  the 
air  through  your  red-hot  platinum  tube  these  active 
powers  are  destroyed,  and  the  sterility  of  your  bulb  of 
urine  has  nothing  surprising  in  it. 

The  partisans  of  spontaneous  generation  had 
often  employed  this  apparently  formidable  reasoning, 
and  Pasteur  thought  it  necessary  to  strengthen  the 
proof  that  the  cotton  wool  through  which  his  air  had 
filtered  was  really  charged  with  germs. 


TI1E  QUESTION   OF  SPONTANEOUS   GENERATION.      101 

By  an  ingenious  method  he  sowed  the  contents  of 
the  cotton  wool  in  the  same  liquids  that  had  been 
rendered  sterile  by  boiling.  The  liquids  became  fertile, 
even  more  fertile  than  if  they  had  been  exposed  to  the 
free  contact  of  atmospheric  air.  Now,  what  was  there 
in  the  dust  contained  in  the  cotton  wool  ?  Only 
amorphous  particles  of  silk,  cotton,  starch;  and, 
along  with  these,  minute  bodies  which,  by  their  trans- 
parency and  their  structure,  were  not  to  be  distin- 
guished from  the  germs  of  microscopic  organisms. 
The  presence  of  imponderable  fluids  could  not  here  be 
pleaded. 

Nevertheless,  fearing  that  determined  scepticism 
might  still  attribute  to  the  cotton  wool  an  influence  of 
some  sort  on  account  of  its  being  an  organised  sub- 
stance, Pasteur  substituted  for  the  stoppers  of  cotton 
wool  stoppers  of  asbestos  previously  heated  to  red- 
ness. The  result  was  the  same. 

"Wishing  still  further  to  dispose  of  the  hypothesis 
that,  in  ordinary  air,  an  unknown  something  existed 
which,  independent  of  germs,  might  be  the  cause 
of  the  observed  microscopic  life,  Pasteur  began  a  new 
series  of  experiments  as  simple  as  they  were  demon- 
strative. Having  placed  a  very  putrescible  infusion — 
in  other  words,  one  very  appropriate  to  the  appearance 
of  microscopic  organisms — in  a  glass  bulb  with  a  long 
neck,  by  means  of  the  blowpipe,  he  drew  out  this  neck 


102  LOUIS  PASTEUR. 

to  a  very  small  diameter,  at  the  same  time  bending 
the  soft  glass  to  and  fro,  so  as  to  form  a  sinuous  tube. 
The  extremity  of  this  narrow  tube  remained  open. 
He  then  boiled  his  liquid  for  some  minutes  until  the 
vapour  of  the  water  came  out  in  abundance  through 
the  narrow  open  tube.  In  these  conditions  the  liquid 
in  the  bulb,  however  putrescible,  is  preserved  indefi- 
nitely without  the  least  alteration.  One  may  handle 
it,  transport  it  from  place  to  place,  expose  it  to  every 
variety  of  climate,  place  it  hi  a  stove  with  a  tempera- 
ture of  thirty  or  forty  degrees,  the  liquid  remains  as 
clear  as  it  was  at  first.  A  slight  oxidation  of  the 
constituents  of  the  liquid,  is  barely  perceptible.  In 
this  experiment  the  ordinary  air,  entering  suddenly 
at  the  first  moment,  finds  in  the  bulb  a  liquid  very 
near  the  boiling  temperature ;  and  when  the  liquid 
is  so  far  cooled  that  it  can  no  longer  destroy  the 
vitality  of  the  germs,  the  entrance  of  the  air  is  cor- 
respondingly retarded,  so  that  the  germs  capable  of 
acting  upon  the  liquid,  and  of  producing  in  it  living 
organisms,  are  deposited  in  the  bends  of  the  still 
moist  tube,  not  coming  into  contact  with  the  liquid 
at  all. 

If,  after  remaining  for  weeks,  months,  or  even 
years,  in  a  heated  chamber,  the  sinuous  neck  of  the 
bulb  is  snipped  off  by  a  file  in  the  vertical  part  of  the 
stem,  after  twenty-four  or  forty-eight  hours  there 
begin  to  appear  mildew,  mucors,  bacteria,  infusoria, 


THE  QUESTION   OF  SPONTANEOUS  GENERATION.       103 

exactly  as  in  the  case  of  infusions  recently  exposed  to 
the  contact  of  ordinary  air. 

The  same  experiments  may  be  repeated  with 
slightly  alkaline  liquids,  such  as  milk,  the  precaution 
being  taken  of  raising  them  to  a  temperature  higher 
than  that  of  100  degrees  Centigrade. 

The  great  interest  of  Pasteur's  method  consists  in 
its  proving  unanswerably  that  the  origin  of  life,  in 
infusions  which  have  been  heated  to  the  boiling  point, 
is  solely  due  to  the  solid  particles  suspended  in  the 
air.  Of  gas,  electricity,  magnetism,  ozone,  things 
known  or  unknown,  there  is  nothing  in  ordinary 
atmospheric  air  which,  apart  from  these  solid  par- 
ticles, can  cause  the  fermentation  or  putrefaction  of 
the  infusions. 

Lastly,  to  convince  the  most  prejudiced  minds, 
and  to  leave  no  contradiction  standing,  Pasteur 
showed  one  of  these  bulbs  with  the  sinuous  neck  which 
he  had  prepared  and  preserved  for  months  and  years. 
The  bulb  was  covered  with  dust.  '  Let  us,'  said  he, 
'  take  up  a  little  of  this  outside  dust  on  a  bit  of  glass, 
porcelain,  or  platinum,  and  introduce  it  into  the 
liquid;  the  following  day  you  will  find  that  the  in- 
fusion, which  up  to  this  time  remained  perfectly  clear, 
has  become  turbid,  and  that  it  behaves  in  the  same 
manner  as  other  infusions  in  contact  with  ordinary 
air.' 

If  the  bulb  be  tilted  so  as  to  cause  a  little  drop 
7 


104  LOUIS  PASTEUR. 

of  the  clear  infusion  to  reach  the  extremity  of  the 
bent  part  of  the  neck  where  the  dust  particles  are 
arrested,  and  if  this  drop  be  then  allowed  to  trickle 
back  into  the  infusion,  the  result  is  the  same — tur- 
bidity supervenes  and  the  microscopic  organisms  are 
developed.  Finally,  if  one  of  those  bulbs  which  have 
stood  the  test  of  months  and  years  without  alteration 
be  several  times  shaken  violently,  so  that  the  external 
air  shall  rush  into  it,  and  if  it  be  then  placed  once 
more  in  the  stove,  life  will  soon  appear  in  it. 

In  1860  the  Academy  of  Sciences  had  offered  a 
prize,  the  conditions  of  which  were  stated  in  the 
following  terms : 

'  To  endeavour  by  well-contrived  experiments  to 
throw  new  light  upon  the  question  of  spontaneous 
generation.'  The  Academy  added  that  it  demanded 
precise  and  rigorous  experiments  equally  well  studied 
on  all  sides;  such  experiments,  in  short,  as  should 
render  it  possible  to  deduce  from  them  results  free 
from  all  confusion  due  to  the  experiments  themselves. 
Pasteur  carried  away  the  prize,  and  no  one,  it  will  be 
acknowledged,  deserved  it  better  than  he.  Neverthe- 
less, to  his  eyes,  the  subject  was  still  beset  with  diffi- 
culties. In  the  hot  discussions  to  which  the  question 
of  spontaneous  generation  gave  rise,  the  partisans  of 
the  doctrine  continually  brought  forward  an  objection 
based  on  an  opinion  already  referred  to,  and  first 
enunciated  by  Gay-Lussac.  As  already  known  to  the 


THE   QUESTION   OF   SPONTANEOUS   GENERATION.      105 

reader,  Gay-Lussac  had  arrived  at  the  conclusion  that, 
in  Appert's  process,  one  condition  of  the  preservation 
of  animal  and  vegetable  substances  consisted  in  the 
exclusion  of  oxygen. 

Even  this  proposition  was  soon  improved  upon, 
and  it  became  a  current  opinion  in  science  that  the 
smallest  bubble  of  oxygen  or  of  air  which  might  come 
in  contact  with  a  preserve  would  be  sufficient  to  start  its 
decomposition.  The  partisans  of  spontaneous  genera- 
tion— the  heterogenists — thenceforward  threw  their 
objections  to  Pasteur  into  this  form  : 

'  How  can  the  germs  of  microscopic  organisms  be 
so  numerous  that  even  the  smallest  bubble  of  air 
contains  germs  capable  of  developing  themselves  in 
every  organic  infusion  ?  If  such  were  the  case  the 
air  would  be  encumbered  with  organic  germs.'  M. 
Pouchet  said  and  wrote  that  they  would  form  a  thick 
fog,  as  dense  as  iron. 

But  Pasteur  showed  that  the  interpretation  of 
Gay-Lussac's  experiment,  with  respect  to  the  possible 
alteration  of  preserves  by  a  small  quantity  of  oxygen 
gas,  was  quite  erroneous.  If,  after  a  certain  time,  an 
Appert  preserve  contains  no  oxygen,  this  is  simply 
because  the  oxygen  has  been  gradually  absorbed  by 
the  substances  of  the  preserve,  which  are  always  more 
or  less  chemically  oxidisable.  But  in  reality  it  is  easy 
to  find  oxygen  in  these  preserves.  Pasteur  did  not 
fail  to  perceive  that  the  interpretation  given  to  Gay- 


106  LOUIS  PASTEUR. 

Lussac's  experiment  was  wrong  in  another  particular. 
He  proved  the  fallacy  of  the  assumption  that  the 
smallest  quantity  of  air  was  always  capable  of  pro- 
ducing microscopic  organisms. 

More  thickly  spread  in  towns  than  in  the  country, 
the  germs  become  fewer  in  proportion  as  they  recede 
from  human  habitations.  Mountains  have  fewer 
than  plains,  and  at  a  certain  height  they  are  very 
rare. 

Pasteur's  experiments  to  prove  these  facts  were 
extremely  simple.  He  took  a  series  of  bulbs  of  about 
a  quarter  of  a  litre  in  capacity,  and,  after  having  half 
filled  the  bulbs  with  a  putrescible  liquid,  he  drew  out 
the  necks  by  means  of  the  blowpipe,  then  he  caused 
the  liquid  to  boil  for  some  minutes,  and  during  the 
ebullition,  while  the  steam  issued  from  the  tapering 
ends  of  the  bulbs,  he  sealed  them  with  the  lamp.  Thus 
prepared,  the  bulbs  can  be  easily  transported.  As 
they  are  empty  of  air — that  which  they  originally 
contained  having  been  driven  out  with  the  steam — 
when  the  sealed  end  of  a  bulb  is  broken  off,  the  air 
rushes  into  the  tube,  carrying  with  it  all  the  germs 
which  this  air  holds  in  suspension.  If  it  is  closed 
again  immediately  afterwards  by  a  flame,  and  if  the 
vessels  are  then  left  to  themselves,  it  is  easy  to 
recognise  those  in  which  a  change  occurs.  Now, 
Pasteur  established  that,  in  whatever  place  the  opera- 
tion might  be  carried  on,  a  certain  number  of  bulbs 


THE  QUESTION   OF  SPONTANEOUS   GENERATION.    107 

would  escape  alteration.  They  must  not,  however,  be 
opened  in  a  room  after  dusting  the  furniture  or  sweep- 
ing the  floor,  for  in  this  case  all  the  bulbs  would  become 
altered  because  of  the  great  quantity  of  germs  raised 
by  the  dusting  and  remaining  suspended  in  the  air. 

Pasteur  started  for  Arbois  with  a  series  of  bulbs. 
Some  he  opened  in  the  country  far  from  all  habitations ; 
others  he  opened  at  the  foot  of  the  mountains  which 
form  the  first  range  of  the  Jura  ;  a  series  of  twenty- 
four  bulbs  was  opened  upon  Mount  Poupet,  at  850 
meters  above  the  level  of  the  sea ;  and,  lastly,  twenty 
others  were  transported  to  the  Montanvert,  near  the 
Mer  de  Glace,  at  an  elevation  of  2,000  meters.  He 
afterwards  brought  his  whole  collection  back  to  Paris, 
and  in  the  month  of  November,  1860,  deposited  them 
on  the  table  at  the  Academy  of  Sciences. 

Of  the  twenty  bulbs  first  opened  in  the  country, 
eight  contained  organised  productions.  Of  the  twenty 
opened  on  the  heights  of  the  Jura,  five  only  were 
altered,  and  of  the  twenty  opened  upon  the  Montan- 
vert during  a  strong  wind  which  blew  from  the 
glacier,  one  alone  was  altered. 

If  a  similar  series  of  experiments  were  made  in  a 
balloon,  it  would  be  found  that  the  air  of  the  higher 
atmosphere  is  absolutely  free  from  germs.  Care 
would,  however,  be  necessary  to  prevent  the  introduc- 
tion of  dust  particles,  which  the  rigging  and  the 
aeronauts  themselves  might  carry  with  them. 


108  LOUIS  PASTEUR. 

But  we  have  not  yet  related  all.  So  far,  all  these 
conclusive  experiments  had  been  made  only  on  organic 
liquids,  very  putrescible  it  is  true,  but  which  had  all 
been  subjected  to  boiling  or  even  to  temperatures 
higher  than  100  degrees  Centigrade.  The  partisans 
of  spontaneous  generation  might  then  be  justified  in 
saying  that  if  the  precaution  had  been  taken  of  putting 
into  contact  with  pure  air  natural  organic  liquids  in  a 
state  compatible  with  the  operations  of  animal  and  vege- 
table life,  the  results  would  have  been  different.  Under 
such  conditions,  life  would  have  appeared  spontaneously 
in  the  production  of  microscopic  organisms.  None  of 
Pasteur's  opponents  had  formulated  this  argument; 
but  Pasteur  himself,  who  had  within  him  an  adversary 
always  present,  always  on  the  alert,  prepared  to  yield 
only  to  accumulated  proofs,  saw  this  objection. 
He  was  not  satisfied  until  he  had  succeeded  in  com- 
pletely refuting  it.  Having  by  means  of  ingenious 
experimental  arrangements  deprived  some  air  of  all 
living  germs,  he  placed  in  contact  with  this  pure 
air  the  most  putrescible  liquids,  particularly  venous 
blood,  arterial  blood,  and  urine.  He  took  these 
liquids  directly  from  the  veins,  the  arteries,  and  the 
bladders  of  animals  in  full  health.  No  alteration 
was  produced.  In  due  time  a  chemical  absorption  of 
small  quantities  of  oxygen  took  place,  but  neither 
fermentation  nor  putrefaction,  nor  the  smallest  deve- 
lopment of  bacteria,  of  vibrios,  or  of  mould.  After 


THE  QUESTION   OF  SPONTANEOUS   GENERATION.       109 

this,  Pasteur  was  able  legitimately  to  exclaim  in  his 
celebrated  lecture  at  the  Sorbonne  : 

'  There  is  not  one  circumstance  known  at  the\ 
present  day  which  justifies  the  assertion  that  micro- 
scopic organisms  come  into  the  world  without  germs 
or  without  parents  like  themselves.  Those  who  main-/ 
tain  the  contrary  have  been  the  dupes  of  illusions  and 
of  ill-conducted  experiments,  tainted  with  errors  whi(j/h 
they  know  not  how  either  to  perceive  or  to  avoijd. 
Spontaneous  generation  is  a  chimera.' 

Pasteur  was  not  alone  in  affirming  this  fixed  con- 
viction. With  the  authority  of  a  judge  delivering 
sentence  in  court,  M.  Flourens,  permanent  Secretary 
of  the  Academy  of  Sciences,  pronounced  these  words 
before  the  whole  Academy  : 

'As  long  as  my  opinion  was  not  formed  I  had 
nothing  to  say;  now  it  is  formed  and  I  can  speak. 
The  experiments  are  decisive.  If  spontaneous  genera- 
tion be  a  fact,  what  is  necessary  for  the  production  of 
animalculse  ?  Air  and  putrescible  liquids.  Now 
Pasteur  puts  together  air  and  putrescible  liquids  and 
nothing  is  produced.  Spontaneous  generation,  then, 
has  no  existence.  Those  who  still  doubt  have  failed 
to  grasp  the  question.' 

But  some  adversaries  remained  incredulous.  When 
Pasteur  had  announced  the  result  of  his  experiments, 
and  brought  before  the  Academy  his  series  of  bulbs, 
Pouchet  and  Joly  declared  that  if  Pasteur  had  opened 


110  LOUIS  PASTEUR. 

his  bulbs  in  the  Jura  and  on  the  Mer  de  Glace,  they, 
on  their  part,  had  been  on  the  top  of  the  Maladetta, 
and  had  proved  there  the  inexactitude  of  Pasteur's 
results. 

Pasteur  asked  to  be  judged  by  the  Academy. 
'A  commission  alone,'  said  he,  'will  terminate  the 
debate.'  The  commission  was  named,  and  the  position 
on  both  sides  was  clearly  stated. 

'  I  affirm,'  said  Pasteur,  '  that  everywhere  it  is 
possible  to  take  from  the  midst  of  the  atmosphere  a 
certain  quantity  of  air  which  contains  neither  egg 
nor  spore,  and  which  does  not  produce  organisms  in 
putrescible  solutions.' 

On  his  side,  M.  Joly  wrote  :  '  If  one  alone  of  your 
bulbs  remains  unaltered  we  shall  loyally  acknowledge 
our  defeat.'  Lastly,  M.  Pouchet,  as  distinct  and 
positive  as  M.  Pasteur,  said :  '  I  affirm  that  in  what- 
ever place  I  take  a  cubic  decimeter  of  air,  when  this 
air  is  placed  in  contact  with  a  fermentable  liquid  en- 
closed in  a  glass  vessel  hermetically  sealed,  the  liquid 
will  become  filled  with  living  organisms.' 

This  double  declaration,  which  excited  at  that  time 
all  the  learned  world,  took  place  in  the  month  of 
January,  1864.  Eager  to  engage  in  the  combat, 
Pasteur  waited  impatiently  for  the  order  of  the  Com- 
mission that  this  experiment,  which  was  to  decide 
everything,  should  be  made.  But  M.  Pouchet  begged 
for  a  postponement,  desiring,  he  said,  to  wait  for  the 


THE  QUESTION   OF   SPONTANEOUS   GENERATION.      Ill 

warm  season.  Pasteur  was  astonished,  but  resigned 
himself  to  the  delay.  The  Commission  and  the 
opponents  met  on  June  15. 

The  Commission  announced,  '  that,  as  the  whole 
dispute  turned  upon  one  simple  fact,  one  single 
experiment  ought  to  be  undertaken,  which  alone 
would  close  the  discussion.' 

The  partisans  of  spontaneous  generation  wished 
nevertheless  to  go  through  the  entire  series  of  their 
experiments.  In  vain  the  Commission  tried  to  per- 
suade them  that  this  would  make  the  judgment  as 
long  as  the  discussion  itself  had  been,  that  all  bore 
upon  one  fact,  and  that  this  fact  could  be  decided  by 
a  single  experiment.  The  heterogenists  would  not 
listen  to  this.  M.  Pouchet  and  M.  Joly  withdrew 
from  the  contest. 

M.  Jamin,  an  exact  and  authorised  historian  of 
these  debates,  observed  that  '  the  heterogenists,  how- 
ever they  may  have  covered  their  retreat,  were  there- 
by self-condemned.  If  they  had  been  sure  of  the 
fact — which  they  were  solemnly  engaged  to  prove, 
under  penalty  of  acknowledging  themselves  defeated — 
they  would  have  hastened  to  demonstrate  it,  for  it 
would  have  been  the  triumph  of  their  doctrine.  People 
do  not  allow  themselves  to  be  condemned  by  default 
except  in  causes  in  which  they  have  no  confidence.' 


112  LOUIS  PASTEUR. 


STUDIES  ON   WINE. 

HAVING  thus  solved  the  problem  of  spontaneous 
generation,  a  problem  which  was  but  a  parenthesis 
forced  upon  his  attention,  Pasteur  returned  to  fer- 
mentation. Guided  by  his  studies  on  vinegar  and 
other  observations  of  detail,  he  undertook  an  inquiry 
into  the  diseases  of  wine.  The  explanations  of  the 
changes  which  wine  was  known  to  undergo  rested 
only  on  hypothesis.  From  the  time  of  Chaptal,  who 
was  followed  by  Liebig  and  Berzelius,  all  the  world 
believed  wine  to  be  a  liquid  in  which  the  various 
constituents  react  upon  each  other  mutually  and 
slowly.  The  wine  was  thought  to  be  continually 
'  working.'  When  the  fermentation  of  the  grape  is 
finished,  equilibrium  is  not  quite  established  between 
the  diverse  elements  of  the  liquor.  Time  is  needed 
for  them  to  blend  together.  If  this  reciprocal  action 
be  not  regular,  the  wine  becomes  bad.  This  was,  in 
other  words,  the  doctrine  of  spontaneity.  Without 
support  from  carefully  reasoned  experiments,  these 
explanations  could  not  satisfy  Pasteur,  especially  at  a 


STUDIES  ON  WINE.  113 

moment  when  he  had  just  been  proving  that  there 
was  nothing  spontaneous  either  in  the  phenomena  of 
fermentation  or  in  animal  and  vegetable  infusions. 

Pasteur  tried  first  of  all  to  show  that  wine  does 
not  '  work '  as  much  as  it  was  supposed  to  do.  Wine 
being  a  mixture  of  different  substances,  among  which 
are  acids  and  alcohol,  particular  ethers  are  no  doubt 
formed  in  it  in  course  of  time,  and  similar  reactions 
perhaps  take  place  between  the  other  constituents  of 
the  liquid.  But  if  the  exactitude  of  such  facts  cannot 
be  denied,  based  as  they  are  upon  general  laws,  con- 
firmed and  extended  by  recent  inquiries,  Pasteur 
thought  that  a  false  application  was  made  of  them 
when  they  were  emploj^ed  to  explain  the  maladies  of 
wine,  the  changes  which  occur  in  it  through  age— in 
a  word,  the  alterations,  whether  good  or  bad,  which 
wines  are  subject  to.  The  '  ageing '  of  wine  soon 
appeared  to  him  to  consist  essentially  in  the  phe- 
nomena of  oxidation,  due  to  the  oxygen  of  the  air 
which  dissolves  and  is  diffused  in  the  wine.  He 
gave  manifest  proofs  of  this.  I  will  only  mention 
one  of  them.  New  wine  inclosed  in  a  glass  vessel 
hermetically  sealed  keeps  its  freshness ;  it  does  not 
'  work,'  it  does  not  '  age.'  Pasteur  demonstrated 
besides,  that  all  the  processes  of  wine-making  are 
explained  by  the  double  necessity  of  oxygenising  the 
wine  to  a  suitable  degree,  and  of  preventing  its  dete- 
rioration. In  seeking  for  the  actual  causes  of  in- 


114  LOUIS  PASTEUK. 

jurious  alterations,  Pasteur,  always  obedient  to  a  pre- 
conceived idea,  while  carefully  controlling  it  with  the 
utmost  rigour  of  the  experimental  method,  asked  him- 
self whether  the  diseases  of  wine  did  not  proceed  from 
organised  ferments,  from  little  microscopic  vegeta- 
tions ?  In  the  observed  alterations,  he  thought,  there 
must  be  some  influences  at  work  foreign  to  the  normal 
composition  of  the  wine. 

This  hypothesis  was  verified.  In  his  hands  the  in- 
jurious modifications  suffered  by  wines  were  shown  to 
be  correlative  with  the  presence  and  the  multiplication 
of  microscopic  vegetations.  Such  growths  alter  the 
wine,  either  by  subtracting  from  it  what  they  need  for 
their  nourishment,  or,  and  principally,  by  forming  new 
products  which  are  the  effect  of  the  multiplication  of 
these  parasites  in  the  mass  of  the  wine. 

Everyone  knows  what  is  meant  by  acid  wine, 
sharp  wine,  sour  wine.  The  former  experiments  of 
Pasteur  had  clearly  shown  that  no  wine  can  become 
acid,  sharp — can,  in  a  word,  become  vinegar — without 
the  presence  of  a  little  microscopic  fungus  known  by 
the  name  of  mycoderma  aceti.  This  little  plant  is  the 
necessary  agent  in  the  condensation  of  the  oxygen  of 
the  air,  and  its  fixation  on  the  alcohol  of  the  wine. 
Chaptal,  who  published  a  volume  on  the  art  of  wine- 
making,  knew  of  the  existence  of  these  mycoderm 
flowers ;  but  to  his  eyes  they  were  only  '  elementary 
forms  of  vegetation,'  which  had  no  influence  whatever 


STUDIES  ON   WINE.  115 

upon  the  quality  of  the  liquid.  Besides  the  myco- 
derma  aceti,  which  is  the  agent  of  acetification,  there 
is  another  mycoderm  called  mycoderma  vini.  This 
one  deposits  nothing  which  is  hurtful  to  the  wine, 
and  its  flowers  are  developed  by  preference  in  new 
wines,  still  immature,  and  preserving  the  astringency 
of  the  first  period  of  their  fabrication. 

The  requirements  of  the  two  sorts  of  flowers  are 
such  that  even  when  the  flower  of  vinegar  is  sown  on 
the  surface  of  a  new  wine,  no  development  takes 
place.  Conversely,  the  mycoderma  vini  sown  on  wines 
that  have  grown  old  in  casks  or  in  bottles  will 
refuse  to  multiply.  The  mycoderma  vini  produces 
no  alteration  in  the  wine ;  it  does  not  turn  the  wine 
acid.  In  proportion  as  the  wine  grows  old  the  flower 
tends  to  disappear,  the  wine  '  despoils '  itself,  to 
use  a  technical  expression ;  physiologically  speaking, 
the  wine  loses  its  aptitude  to  nourish  the  mycoderma 
vini,  which,  finding  itself  progressively  deprived  of 
appropriate  nourishment,  fades  and  withers.  But  it 
is  then  that  the  mycoderma  aceti  appears,  and  multi- 
plies with  a  facility  so  much  the  greater  that  it  draws 
its  first  nourishment  from  the  cells  of  the  mycoderma 
vini.  The  mycoderma  aceti  has  played  so  large  a  part 
in  the  early  pages  of  this  book  that  it  is  not  necessary 
to  go  back  upon  it  here. 

There  is  another  disease  very  common  among 
wines  when  the  great  heat  of  summer  begins  to  make 


116  LOUIS  PASTEUR. 

itself  felt  in  the  vintage  tubs.  The  wine  is  said  to 
turn,  to  rise,  to  spurt.  The  wine  becomes  slightly 
turbid  and  at  the  same  time  flat  and  piquant. 
When  it  is  poured  into  a  glass,  very  small  bubbles 
of  gas  form  like  a  crown  upon  the  surface.  On 
placing  the  glass  between  the  eye  and  the  light 
and  slightly  shaking  it,  one  can  distinguish  silky 
waves  shifting  about  and  moving  in  different  direc- 
tions in  the  liquid.  When  the  turned  wine  is  in  a 
cask,  it  is  not  unusual  to  see  the  bottom  of  the  cask 
bulge  a  little,  and  sometimes  a  leakage  takes  place  at 
the  joints  of  the  staves.  If  a  little  opening  is  made, 
the  wine  spurts  out,  and  that  is  the  reason  why  the 
wine  is  said  to  spurt. 

Authors  who  have  written  on  the  subject  of 
wine  attributed  this  malady  to  the  rising  of  the  lees. 
They  believed  that  the  deposit  which  always  exists  in 
greater  or  less  quantities  in  the  lower  part  of  the 
cask  rises  and  spreads  itself  into  all  the  mass  of  the 
wine. 

Nothing  can  be  more  inexact.  If  this  phenomenon 
is  sometimes  produced — that  is  to  say,  if  the  deposit 
rises  into  the  mass  of  wine — the  effect  is  due  to  a 
sudden  diminution  of  the  atmospheric  pressure,  as  in 
times  of  storm,  for  example.  As  the  wine  is  always 
charged  with  carbonic  acid  gas,  which  it  holds  in 
solution  from  the  moment  of  fermentation,  one  can 
conceive  that  a  lowering  of  barometric  pressure  would 


STUDIES   ON  WINE.  117 

cause  the  escape  of  some  bubbles  of  carbonic  acid. 
These  bubbles,  rising  from  the  lower  part  of  the  cask, 
may  disturb  a  portion  of  the  deposit,  which  then  mixes 
with  the  wine  and  renders  it  turbid.  But  the  real 
cause  of  the  disease  is  quite  different.  The  turbidity 
is  without  exception  due  to  the  presence  of  little  fila- 
ments of  an  extreme  tenuity,  about  a  thousandth  part 
of  a  millimeter  in  diameter.  Their  length  is  very 
variable.  It  is  these  which,  when  the  wine  is  agitated, 
give  rise  to  the  silky  waves  just  referred  to.  Often  the 
deposit  of  the  casks  leaves  a  swarm  of  these  filaments 
entangled  in  each  other,  forming  a  glutinous  mass, 
which  under  the  microscope  is  seen  to  be  composed 
entirely  of  these  little  filaments.  In  acting  upon 
certain  constituents  of  the  wine,  particularly  upon  the 
tartar,  this  ferment  generates  carbonic  acid.  The 
phenomenon  of  spurting  is  then  produced,  because 
when  the  cask  is  closed  the  internal  pressure  of  the 
liquid  augments.  The  sparkling  and  the  crown  of 
little  gas-bubbles,  observed  when  the  turned  wine  is 
poured  out  into  a  glass,  is  similarly  explained.  In 
a  word,  the  disease  of  turned  wine  is  nothing  else 
than  a  fermentation,  due  to  an  organised  ferment 
which,  without  any  doubt,  proceeds  originally  from 
germs  existing  on  the  surface  of  the  grapes  at  the 
moment  of  gathering  them,  or  on  spoilt  grapes  such 
as  are  found  in  every  vintage.  It  is  very  rare 
not  to  find  this  parasite  of  turned  wine  in  the  de- 


118  LOUIS  PASTEUR 

posit  of  the  wine  at  the  bottom  of  the  casks,  but 
the  parasite  is  not  troublesome  unless  it  multiplies 
very  largely.  Pasteur  found  the  means  of  prevent- 
ing this  multiplication  by  a  very  simple  remedy, 
equally  applicable  to  other  diseases  of  wines,  such 
as  that  of  bitterness  or  greasiness  (maladie  de  la 
graisse). 

Many  wines  acquire  with  age  a  more  or  less  bitter 
taste,  sometimes  to  a  degree  which  renders  them 
unfit  for  consumption.  Eed  wines,  without  exception, 
are  subject  to  this  disease.  It  attacks  by  preference 
wines  of  the  best  growth,  and  particularly  the  finest 
wines  of  the  Cote-d'Or.  It  is  once  more  a  little  fila- 
mented  fungus  which  works  the  change ;  and  not 
only  does  it  cause  in  the  wine  a  bitterness  which  little 
by  little  deprives  it  of  all  its  better  qualities,  but  it 
forms  in  the  bottles  a  deposit  which  never  adheres 
to  the  glass,  but  renders  the  wine  muddy  or  turbid. 
It  is  in  this  deposit  that  the  filaments  of  the  fungus 
float.  If  white  wines  do  not  suffer  from  this  disease 
of  bitterness,  they  are  exposed,  particularly  the  white 
wines  of  Orleans  and  of  the  basin  of  the  Loire,  to  the 
disease  of  greasiness.  The  wines  lose  their  limpidity  ; 
they  become  flat  and  insipid  and  viscous,  like  oil  when 
poured  out.  The  disease  declares  itself  in  the  casks  or 
in  the  best-corked  bottles.  M.  Pasteur  has  discovered 
that  the  greasiness  of  wines  is  likewise  produced  by  a 
special  ferment,  which  the  microscope  shows  to  be 


STUDIES  ON   WINE.  119 

formed  of  filaments,  like  the  ferments  of  the  preceding 
diseases,  but  differing  in  structure  from  the  other 
organisms,  and  in  their  physiological  action  on  tho 
wine. 

In  short,  according  to  Pasteur's  observations,  the 
deterioration  of  wines  should  not  in  any  case  be  attri- 
buted to  a  natural  working  of  the  constituents  of  the 
wine,  proceeding  from  a  sort  of  interior  spontaneous 
movement,  which  would  only  be  affected  by  varia- 
tions of  temperature  or  atmospheric  pressure.  They 
are,  on  the  contrary,  exclusively  dependent  on  the 
development  of  microscopic  organisms,  the  germs  of 
which  exist  in  the  wine  from  the  moment  of  the 
original  fermentation  which  gave  it  birth.  What  vast 
multitudes  of  germs  of  every  kind  must  there  not  be 
introduced  into  every  vintage  tub  !  What  modifica- 
tions do  we  not  meet  with  in  the  leaves  and  in  the 
fruit  of  each  individual  spoilt  vine  !  How  numerous 
are  the  varieties  of  organic  dust  to  be  found  on  the 
stems  of  the  bunches,  on  the  surface  of  the  grapes,  on 
the  implements  of  the  grape  gatherers  !  What  varieties 
of  moulds  and  mildews  !  A  vast  proportion  of  these 
germs  are  evidently  sterilised  by  the  wine,  whose  com- 
position, being  at  the  same  time  acid,  alcoholic,  and 
devoid  of  air,  is  so  little  favourable  to  life.  But  is  it 
to  be  wondered  at  that  some  of  these  exterior  germs, 
so  numerous,  and  possessing  in  a  more  or  less  marked 
degree  the  anaerobic  character,  should  find  at  certain 


120  LOUIS  PASTEUR. 

moments,  in  the  state  of  the  wine,  the  right  conditions 
for  their  existence  and  multiplication  ? 

The  cause  of  these  alterations  having  been  found,  a 
mode  of  preventing  the  development  of  all  these  para- 
sites had  still  to  be  sought.  Pasteur's  first  endeavour 
was  to  discover  some  substance  which  would  be  anta- 
gonistic to  the  life  of  these  ferments  of  disease,  while 
harmless  to  the  wine  itself,  and  devoid  of  any  special 
smell  or  taste.  But  in  this  research  success  was 
dependent  on  too  many  conditions  to  be  easily  attain- 
able. After  some  fruitless  trials,  the  thought  occurred 
to  Pasteur  of  having  recourse  to  heat.  He  soon 
ascertained  that,  to  secure  wine  from  all  ulterior 
changes,  it  sufficed  to  raise  it,  for  some  instants 
only,  to  a  temperature  of  from  fifty-five  to  sixty 
degrees.  His  experiments  were  first  directed  upon 
the  disease  of  '  bitterness.'  He  procured  some  of  the 
best  wines  of  Burgundy,  wines  of  Beaune,  and  of 
Pomard,  of  different  years— 1858,  1862,  and  1863. 
Twenty-five  bottles  were  left  standing  forty-eight 
hours  to  allow  all  the  particles  suspended  in  the  wine 
to  settle ;  for,  however  clear  wine  may  be,  it  always 
produces  a  slight  deposit.  Pasteur  then  decanted  the 
wine  with  minute  care,  by  means  of  a  syphon  of  slow 
delivery.  This  last  precaution  was  necessary  to  pre- 
vent the  deposit  from  being  stirred  up.  When  there 
remained  in  each  bottle  only  one  cubic  centimeter  of 


STUDIES   ON   WINE.  121 

liquid,  Pasteur  shook  the  bottle,  and  then  examined 
with  the  microscope  the  residue  of  each  bottle.  He 
perceived  in  each  case  distinct  filaments  of  ferment. 
The  wines,  however,  were  not  in  the  least  bitter  to 
the  taste,  but  the  germs  of  a  possible  evil  were  there 
— an  evil  which  would  have  been  first  detected  by  the 
palate  when  the  little  fungus  had  fully  developed. 

Without  uncorking  it,  Pasteur  then  heated  a 
bottle  of  each  of  these  wines.  The  heating  was  carried 
to  a  temperature  of  sixty  degrees  (140°  Fahr.).  After 
the  cooling  of  the  bottles  he  laid  them  by  the  side  of 
other  unheated  bottles  of  the  same  wines  in  a  cellar, 
the  temperature  of  which  varied  in  summer  between 
thirteen  and  seventeen  degrees.  Every  fifteen  days 
Pasteur  inspected  them.  Without  uncorking  the 
bottles,  he  held  them  up  against  the  light,  so  that  he 
could  see  the  sediment  at  the  bottom  of  each  bottle, 
and  thus  detect  the  least  formation  of  deposit.  In  less 
than  six  weeks,  particularly  in  the  wine  of  1863,  a 
very  perceptible  floating  deposit  began  to  form  in  all  the 
unheated  bottles.  These  deposits  gradually  augmented, 
and  on  examining  them  with  the  microscope  they  were 
seen  to  be  formed  of  organised  filaments,  mixed  some- 
times with  a  little  colouring  matter  which  had  become 
insoluble.  No  deposit  appeared  in  the  heated  bottles. 

The  idea  of  heating  wines  does  not  belong  to 
Pasteur.  Those  who  love  to  search  into  questions  of 


122  LOUIS  PASTEUR 

priority  will  find  described  in  the  works  of  Latin 
agriculturists  various  methods  for  the  preservation 
of  wine,  based  on  the  employment  of  heat.  To  give 
the  wine  durability,  they  sometimes  added  to  the 
vintage  variable  quantities  of  boiled  must,  reduced  to 
half  or  two  thirds,  in  which  orris,  myrrh,  cinnamon, 
white  resin,  and  other  ingredients,  were  infused.  But, 
to  cite  examples  nearer  our  own  time,  Appert,  whose 
preserves  have  become  so  popular,  relates  that  he  sent 
to  St.  Domingo  some  bottles  of  Beaune  which  had 
been  previously  heated  to  seventy  degrees,  and  that 
he  compared,  on  their  return  into  France,  two  bottles 
of  this  wine  with  a  bottle  which  had  remained  at 
Havre,  and  also  with  other  bottles  of  the  same  wine 
which  had  remained  in  his  cellar,  neither  of  which  had 
undergone  the  operation  of  heating.  The  superiority 
of  the  wine  which  came  from  St.  Domingo,  said 
Appert,  was  incontestable.  Nothing  could  equal  its 
delicacy  or  its  perfume.  But  Appert  did  not  by  any 
means  describe  the  wine  of  the  two  bottles  which  re- 
mained in  France  as  either  injured  or  diseased.  His 
remark  was  based  upon  an  incomplete  observation. 
It  simply  stated  the  fact,  which  indeed  was  previously 
known,  that  a  long  voyage,  added  to  the  employment  of 
heat,  had  an  excellent  effect  upon  the  Beaune.  This  in- 
cident had  been  so  completely  forgotten,  that  it  was  only 
in  1865  that  Pasteur,  during  the  historical  researches 
which  preceded  his  '  Etudes  sur  le  vin,'  accidentally 


STUDIES  ON   WINE.  123 

met  with  this  story  of  the  bottles  of  St.  Domingo,  and 
hastened  to  communicate  it  to  the  Academy.     But 
in  reference  to  this  question  of  heating,  a  discussion 
arose  as  to  priority,  which  was  quite  unexpected  by 
him.     A  Burgundian  wine  grower,  M.  de  Vergnette, 
having  first  proposed  the  congealing  of  wines  as  a  pro- 
tective influence,  had  afterwards  spoken,  without  much 
precision,  of  heat  as  another  means  of  preservation. 
On  this  ground  he  claimed  for  himself  a  great  part  of 
the  invention  of  Pasteur's  process.    '  If,  after  having 
subjected  some  specimens  of  wines  which  are  to  be  sent 
abroad  to  the  ordeal  of  heating,'  said  M.  de  Vergnette, 
*  one  sees  that  they  have  been  able  to  resist  the  action 
of  the  heat,  then  they  may  safely  be  shipped.     In  the 
contrary  case  they  ought  not  to  be  sent.'    According  to 
M.  de  Vergnette,  it  was  to  the  composition  of  the  wine, 
its  robust   condition,  and   good  constitution,  that  it 
owed   its   power  of  supporting  the   heating  process. 
Pasteur  had  no  difficulty  in  demonstrating  that  these 
assertions   are   contradicted    by   experiment.      Wine 
never   changes  by  the  moderate  application  of  heat 
when  air  is  excluded  ;  and   it   is   precisely  when  of 
doubtful  soundness  that  it  should  be  subjected  to  the 
process  of  heating.     This  operation  does  not  alter  it 
any  more  than  would  be  the  case  if  it  were  in  a  perfectly 
healthy  state.     All  wines  may  undergo  the  action  of 
heat  without  the  least  deterioration,  and  one  minute's 
heating  at  the  proper  temperature  suffices  to  insure 


124  LOUIS  PASTEUK. 

the  preservation  of  every  kind  of  wine.  Thanks  to 
this  operation,  the  weakest  wine,  the  most  disposed  to 
turn  sour,  to  become  greasy,  or  to  be  threatened  with 
bitterness,  is  insured  against  injurious  change. 

Nothing  is  more  simple  than  to  realise  the  con- 
dition of  heating  in  bottles.  After  having  firmly  tied 
down  the  corks,  the  bottles  are  placed  in  a  water-bath. 
An  iron  basket  is  here  useful.  The  water  ought  to 
rise  up  to  the  wire  of  the  cork.  Among  these  bottles 
is  placed  a  bottle  of  water,  into  which  the  bulb  of  a 
thermometer  is  plunged.  The  bath  being  heated,  as 
soon  as  the  thermometer  marks  fifty  or  sixty  degrees 
Centigrade,  the  basket  is  withdrawn.  The  subsequent 
soundness  of  the  wine  is  thus  insured. 

But  if  Pasteur  had  overlooked  nothing  in  his  efforts 
to  prevent  or  arrest  the  evil  changes  of  wine,  he  still 
saw  that  full  confidence  was  not  felt  in  the  efficacy  of  a 
process  which  must,  it  was  thought,  damage  the  taste, 
or  the  colour,  or  the  limpidity  of  the  wine.  After 
having  invited  the  judgment  of  people  in  society,  whose 
preference,  if  they  felt  any,  was  generally  for  the  heated 
wines,  Pasteur  wished  to  have  a  more  decisive  opinion. 
He  addressed  himself  first  to  wine  merchants  and 
others  practised  in  detecting  the  smallest  peculiarities 
of  wines ;  and  afterwards  he  organised  a  grand  experi- 
ment in  tasting.  On  November  16, 1865,  a  sub-com- 
mission, nominated  by  the  representative  commission 
of  the  wholesale  wine-sellers  of  Paris,  repaired  to  the 


STUDIES  ON  WINE.  125 

ficole  Normale  and  examined  a  considerable  number 
of  specimens.  After  a  series  of  tastings,  which  recog- 
nised, if  not  a  superiority  over  the  heated  wines,  at  least 
a  shade  of  imperceptible  flavour,  which,  however,  it 
was  admitted,  would  escape  nine-tenths  of  the  con- 
sumers, Pasteur,  fearing  that  there  remained  still  in 
the  mind  of  the  majority  of  the  commission  a  slight 
prejudice  against  the  operation  of  heating,  and  that 
imagination,  moreover,  had  some  share  in  deter- 
mining shades  of  flavour,  proposed  that  at  the  next 
sitting  there  should  be  no  indication  which  of  the 
samples  of  wine  had  been  heated  and  which  had  not. 
The  commission,  having  no  other  desire  than  to  arrive 
at  the  truth,  at  once  accepted  this  proposition. 

The  resulting  uncertainty  as  to  whether  the  heated 
or  the  unheated  wines  were  to  be  preferred  was  so  abso- 
lute as  to  be  comical.  It  is  unnecessary  to  say  that  the 
heated  wines  had  not  experienced  the  least  alteration. 
At  a  certain  point  Pasteur,  who  was  astonished  at  the 
extraordinary  delicacy  of  the  palate  of  these  tasters, 
employed  a  little  trickery.  He  offered  them  two  speci- 
mens absolutely  identical,  taken  out  of  the  same  bottle. 
There  were  preferences,  very  slight  it  is  true,  but  pre- 
ferences gravely  expressed  for  one  or  the  other  glass. 
The  commission,  making  allusion  in  its  report  to  this 
special  tasting  experiment,  was  the  first  to  allow  with 
a  good  grace  that  the  differences  between  the  heated 
and  non-heated  wines  were  insignificant,  imperceptible 


12  o  LOUIS  PASTEUR 

if  they  existed,  and  that  the  imagination — added  the 
report — was  not  without  considerable  influence  in  the 
tasting,  since  the  members  of  the  commission  had 
themselves  fallen  into  a  little  experimental  snare. 

Thus  Pasteur,  after  having  revealed  the  causes 
which  determine  the  alterations  of  wines,  had  found 
the  means  of  practically  neutralising  them.  By  the 
application  of  heat,  and  without  producing  any  change 
in  the  colour  or  flavour  of  the  wines,  he  had  been  able  to 
insure  their  limpidity,  and  to  render  them  capable  of 
being  indefinitely  preserved  in  well-closed  vessels.  If 
these  wines,  being  afterwards  exposed  too  long  to  the 
air,  were  again  threatened  with  alteration,  it  was  be- 
cause the  air  brought  to  them  new  living  germs  of 
those  ferments  which  had  been  destroyed  by  the  heat. 
But  germs  from  this  source  are  so  trifling  compared 
with  those  contained  in  the  wine  itself,  that  one  may 
almost  say  the  heating  process  renders  the  wine  un- 
alterable even  after  it  has  been  rebottled  in  contact 
with  the  air.  Thus,  by  a  series  of  experiments  which 
left  nothing  to  chance,  one  of  the  greatest  economic 
questions  of  the  day  was  solved.  Wines  could  be 
kept  or  transported  into  all  countries  without  losing 
their  flavour  or  their  perfume.  These  experiments  of 
the  laboratory  were  destined  to  have  an  extensive 
application ;  for  very  soon  arrangements  were  made 
for  heating  wine  in  barrels,  the  inquiry  thereby  as- 
suming the  proportions  of  a  public  benefit. 


THE  SILKWORM-DISEASE. 

THE  life  of  the  population  of  certain  departments 
in  the  South  of  France  hangs  on  the  existence  of 
silkworms.  In  each  house  there  is  nothing  to  be  seen 
but  hurdles,  over  which  the  worms  crawl.  They  are 
placed  even  in  the  kitchens,  and  often  in  well-to-do 
families  they  occupy  the  best  rooms.  In  the  largest 
cultivations,  regular  stages  of  these  hurdles  are  raised 
one  above  the  other  in  immense  sheds,  under  roofs  of 
disjointed  tiles,  where  thousands  and  thousands  of 
silkworms  crawl  upon  the  litters  which  they  have  the 
instinct  never  to  leave.  Great  or  small,  the  silkworm- 
rearing  establishments  exist  everywhere.  When  people 
accost  each  other,  instead  of  saying  '  How  are  you  ?  ' 
they  say  '  How  are  the  silkworms  ?  '  In  the  night  they 
get  up  to  feed  them  or  to  keep  up  around  them  a 
suitable  temperature.  And  then  what  anxiety  is 
felt  at  the  least  change  of  weather !  Will  not  the 
mulberry  leaves  be  wet  ?  Will  the  worms  digest  well  ? 
Digestion  is  a  matter  of  great  importance  to  the  health 

of  the  worms,  which  do  nothing  all  their  lives  but  eat ! 
8 


128  LOUIS  PASTEUR. 

Their  appetites  become  especially  insatiable  during 
the  last  days  of  rearing.  All  the  world  is  then  astir, 
day  and  night.  Sacks  of  leaves  are  incessantly 
brought  in  and  spread  out  on  the  litters.  Sometimes 
the  noise  of  the  worms  munching  these  leaves  resembles 
that  of  rain  falling  upon  thick  bushes.  With  what 
impatience  is  the  moment  waited  for  when  the  worms 
arrive  at  the  last  moulting  !  Their  bodies  swollen 
with  silk,  they  mount  upon  the  brambles  prepared 
for  them,  there  they  shut  themselves  up  in  then*  golden 
prisons  and  become  chrysalides.  What  days  of  rejoicing 
are  those  in  which  the  cocoons  are  gathered ;  when, 
to  use  the  words  of  Olivier  de  Serres,  the  silk  harvest 
is  garnered  in  ! 

Just  as  in  all  agricultural  harvests,  this  ingather- 
ing of  the  silk  is  exposed  to  many  risks.  Nearly 
always,  however,  it  pays  the  cultivator  for  his  trouble, 
and  sometimes  pays  him  largely.  But  in  1849,  after 
an  exceptionally  good  year,  and  without  any  atmo- 
spheric conditions  to  account  for  the  fact,  a  number 
of  cultivations  entirely  broke  down.  A  disease  which 
little  by  little  took  the  proportions  of  an  epidemic 
fell  upon  the  silkworm  nurseries.  Worms  hardly 
hatched,  and  worms  arrived  at  the  last  moulting,  were 
equally  stricken  in  large  numbers.  It  mattered  little 
in  what  phase  the  silkworm  happened  to  be  :  in  all  it 
was  assailable  by  the  evil. 

There  is  hardly  a  schoolboy  who  has  not  reared  in 


THE  SILKWORM-DISEASE.  129 

the  recesses  of  his  desk  some  five  or  six  silkworms,  feed- 
ing them,  in  default  of  mulberry  leaves,  with  leaves  of 
lettuce  or  salsify.  Therefore  it  is  hardly  necessary  to 
remind  my  readers  how  the  silkworm  is  born,  grows, 
and  is  transformed.  Coming  out  of  its  egg,  which  is 
called  a  grain,  because  of  its  resemblance  to  a  small 
vegetable  seed,  the  silkworm  appears  in  the  first  fine 
days  of  spring.  It  does  not  then  weigh  more  than 
one  or  two  milligrammes.  Little  by  little  its  size  and 
its  activity  augment.  The  seventh  day  after  its  birth 
it  rests  on  a  leaf  and  appears  to  sleep.  It  remains 
thus  for  nearly  thirty  hours.  Presently,  its  head 
moves,  as  if  it  did  not  belong  to  the  rest  of  the  body, 
and  under  the  skin  of  this  head  appears  a  second 
quite  new  head.  Just  as  if  it  came  out  of  a  case,  the 
silkworm  disengages  itself  from  its  old  withered  skin. 
Here  are  its  front  feet,  there  the  false  feet  (faussespattes), 
which  it  carries  behind.  At  length  the  worm  is  quite 
complete.  It  rests  a  while  and  then  begins  to  eat. 
At  the  end  of  a  few  days  new  sleep,  new  skin,  new 
shedding  of  the  skin,  then  a  third,  and  then  a  fourth 
metamorphosis.  About  eight  days  after  the  fourth 
shedding  of  its  skin,  the  worm  ceases  to  eat,  its  body 
becomes  more  slender,  more  transparent ;  it  seeks  to 
leave  its  litter,  it  raises  its  head  and  appears  uneasy. 
Some  twigs  of  dried  heather  are  then  arranged  for 
it  to  fasten  upon ;  these  it  climbs,  never  to  descend 
again.  It  spins  its  cocoon  and  becomes  a  chrysalis. 


130  LOUIS  PASTEUE. 

When  the  worms  of  a  cultivation  have  all  spun 
their  cocoons,  they  are  smothered  in  a  steam  stove, 
and,  after  being  dried  in  the  sun,  they  are  handed 
over  to  the  spinners.  If  it  is  desired  to  reserve  some 
of  the  cocoons  for  seed,  instead  of  being  smothered, 
they  are  strung  together  in  chaplets.  After  about 
three  weeks,  the  moth  comes  out  of  its  chrysalis.  It 
pierces  the  cocoon  by  means  of  a  liquid  which  issues 
from  its  mouth,  and  which  has  the  property  of  so 
softening  the  silk  that  the  moth  is  able  to  pass  through 
the  cocoon.  It  has  hardly  dried  itself  and  developed 
its  wings  when  the  males  and  females  pair  for  several 
hours.  Then  the  females  lay  their  eggs,  of  which  they 
can  produce  from  four  to  six  hundred.  These  are  all 
the  phases  through  which  silkworms  pass  in  the  space 
of  two  months. 

In  the  epidemic  which  ravaged  the  silkworm  nur- 
series in  1849  the  symptoms  were  numerous  and 
changeable.  Sometimes  the  disease  exhibited  itself 
immediately.  Many  of  the  eggs  were  sterile,  or  the 
worms  died  during  the  first  days  of  their  existence. 
Often  the  hatching  was  excellent,  and  the  worms  ar- 
rived at  their  first  moulting,  but  that  moulting  was  a 
failure.  A  great  number  of  the  worms,  taking  little 
nourishment  at  each  repast,  remained  smaller  than 
the  others,  having  a  rather  shining  appearance  and  a 
blackish  tint.  Instead  of  all  the  worms  going  through 


THE   SILKWORM-DISEASE.  131 

the  phases  of  this  first  moulting  together,  as  is  usually 
the  case  in  a  batch  of  silkworms,  they  began  to  present  a 
marked  inequality,  which  displayed  itself  more  and  more 
at  each  successive  moulting.  Instead  of  the  worms 
swarming  on  the  tables,  as  if  their  number  was  uniformly 
augmenting,  empty  spaces  were  everywhere  seen ; 
every  morning  corpses  were  collected  on  the  litters. 

Sometimes  the  disease  manifested  itself  under  still 
more  painful  circumstances.  The  batch  would  pro- 
gress favourably  to  the  third,  and  even  to  the  fourth 
moulting,  the  uniform  size  and  the  health  of  the 
worms  leaving  nothing  to  be  desired ;  but  after  the 
fourth  moulting  the  alarm  of  the  husbandman  began. 
The  worms  did  not  turn  white,  they  retained  a  rusty 
tint,  their  appetite  diminished,  they  even  turned 
away  from  the  leaves  which  were  offered  to  them. 
Spots  appeared  on  their  bodies,  black  bruises  irregu- 
larly scattered  over  the  head,  the  rings,  the  false  feet, 
and  the  spur.  Here  and  there  dead  worms  were 
to  be  seen.  On  lifting  the  litter,  numbers  of  corpses 
would  be  found.  Every  batch  attacked  was  a  lost 
batch.  In  1850  and  1851  there  were  renewed  failures. 
Some  cultivators,  discouraged,  attributed  these  acci- 
dents to  bad  eggs,  and  got  their  supplies  from  abroad. 

At  first  everything  went  as  well  as  could  be 
wished.  The  year  1853,  in  which  many  of  these 
eggs  were  reared  in  France,  was  one  of  the  most 
productive  of  the  century.  As  many  as  twenty-six 


132  LOUIS  PASTEUE. 

millions  of  kilogrammes  of  cocoons  were  collected, 
which  produced  a  revenue  of  130,000,000  francs. 
But  the  year  following,  when  the  eggs  produced  by 
the  moths  of  these  fine  crops  of  foreign  origin  were 
tried,  a  singular  degeneracy  was  immediately  recog- 
nised. The  eggs  were  of  no  more  value  than  the  French 
eggs.  It  was  in  fact  a  struggle  with  an  epidemic. 
How  was  it  to  be  arrested  ?  Would  it  be  always 
necessary  to  have  recourse  to  foreign  seed  ?  and 
what  if  the  epidemic  spread  into  Italy,  Spain,  and  the 
other  silk  cultivating  countries  ? 

The  thing  dreaded  came  to  pass.  The  plague 
spread;  Spain  and  Italy  were  smitten.  It  became 
necessary  to  seek  for  eggs  in  the  Islands  of  the 
Archipelago,  in  Greece,  or  in  Turkey.  These  eggs,  at 
first  very  good,  became  infected  in  their  turn  in  their 
native  country ;  the  epidemic  had  spread  even  to  that 
distance.  The  eggs  were  then  procured  from  Syria 
and  the  provinces  of  the  Caucasus.  The  plague 
followed  the  trade  in  the  eggs.  In  1864  all  the  culti- 
vations, from  whatever  corner  of  Europe  they  came, 
were  either  diseased  or  suspected  of  being  so.  In  the 
extreme  East,  Japan  alone  still  remained  healthy. 

Agricultural  societies,  governments,  all  the  world 
was  preoccupied  with  this  scourge  and  its  invading 
march.  It  was  said  to  be  some  malady  like  cho- 
lera which  attacked  the  silkworms.  Hundreds  of 
pamphlets  were  published  each  year.  The  most 


THE  SILKWORM-DISEASE.  133 

foolish  remedies  were  proposed,  as  quite  infallible — 
from  flowers  of  sulphur,  cinders,  and  soot  spread  over 
the  worms,  or  over  the  leaves  of  the  mulberry,  to 
gaseous  fumigations  of  chlorine,  of  tar,  and  of  sul- 
phurous acid.  Wine,  rum,  absinthe,  were  prescribed 
for  the  worms,  and  after  the  absinthe  it  was  advised 
to  try  creosote  and  nitrate  of  silver.  In  1863  the 
Minister  of  Agriculture  signed  an  agreement  with  an 
Italian  who  had  offered  for  purchase  a  process  destined 
to  combat  the  disease  of  the  silkworms,  by  which 
he  (the  Minister)  engaged  himself,  in  case  the  efficacy 
of  the  remedy  was  established,  to  pay  500,000  francs 
as  an  indemnity  to  the  Italian  silk  cultivator.  Ex- 
periments were  instituted  in  twelve  departments,  but 
without  any  favourable  result.  In  1865  the  weight 
of  the  cocoons  had  fallen  to  four  million  kilogrammes. 
This  entailed  a  loss  of  100,000,000  francs. 

The  Senate  was  assailed  by  a  despairing  petition 
signed  by  3,600  mayors,  municipal  councillors,  and 
capitalists  of  the  silk-cultivating  departments.  The 
great  scientific  authority  of  M.  Dumas,  his  knowledge 
of  silk  husbandry,  his  sympathy  for  one  of  the  depart- 
ments most  severely  smitten,  the  Gard,  his  own  native 
place,  all  contributed  to  cause  him  to  be  nominated 
Reporter  of  the  Commission.  While  drawing  up  his 
report  the  idea  occurred  to  him  of  trying  to  persuade 
Pasteur  to  undertake  researches  as  to  the  best  means 
of  combating  the  epidemic. 


134  LOUIS  PASTEUR. 

Pasteur  at  first  declined  this  offer.  It  was  at  the 
moment  when  the  results  of  his  investigations  on 
organised  ferments  opened  to  him  a  wide  career ;  it 
was  at  the  time  when,  as  an  application  of  his  latest 
studies,  he  had  just  recognised  the  true  theory  of  the 
fabrication  of  vinegar,  and  had  discovered  the  cause  of 
the  diseases  of  wines  ;  it  was,  in  short,  at  the  moment 
when,  after  having  thrown  light  upon  the  question  of 
spontaneous  generation,  the  infinitely  little  appeared 
infinitely  great.  He  saw  living  ferments  present  every- 
where, whether  as  agents  of  decomposition  employed  to 
render  back  to  the  atmosphere  all  that  had  lived,  or 
as  direct  authors  of  contagious  maladies.  And  now 
it  was  proposed  to  him  to  quit  this  path,  where  his 
footing  was  sure,  which  offered  him  an  unlimited 
horizon  in  all  directions,  to  enter  on  an  unknown 
road,  perhaps  without  an  outlet.  Might  he  not  expose 
himself  to  the  loss  of  months,  perhaps  of  years,  in 
barren  efforts  ? 

M.  Dumas  insisted.  '  I  attach,'  said  he  to  his  old 
pupil,  now  become  his  colleague  and  his  friend,  '  an 
extreme  value  to  your  fixing  your  attention  upon 
the  question  which  interests  my  poor  country.  Its 
misery  is  beyond  anything  that  you  can  imagine.' 

'But  consider,'  said  Pasteur,  'that  I  have  never 
handled  a  silkworm.' 

*  So  much  the  better,'  replied  M.  Dumas.  '  If  you 
know  nothing  about  the  subject,  you  will  have  no 


THE  SILKWOKM-DISEASE.  135 

other  ideas  than  those  which  come  to  you  from  your 
own  observations.' 

Pasteur  allowed  himself  to  be  persuaded,  less  by  the 
force  of  these  arguments  than  by  the  desire  to  give 
his  illustrious  master  a  proof  of  his  profound  deference. 

As  soon  as  the  promise  was  given  and  the  resolu- 
tion made  to  go  to  the  South,  Pasteur  thought  over 
the  method  to  be  employed  in  the  pursuit  of  the 
problem.  Certainly,  amidst  the  labyrinth  of  facts  and 
opinions,  it  was  not  hypotheses  which  were  wanting. 
For  seventeen  years  they  had  been  rising  up  on  all 
sides. 

One  of  the  most  recent  and  the  most  comprehen- 
sive memoirs  upon  the  terrible  epidemic  had  been 
presented  to  the  Academy  of  Sciences  by  M.  de  Quatre- 
fages.  One  paragraph  of  this  paper  had  forcibly 
struck  Pasteur.  M.  de  Quatrefages  related  that  some 
Italian  naturalists,  especially  Filippi  and  Cornalia, 
had  discovered  in  the  worms  and  moths  of  the  silk- 
worm minute  corpuscles  visible  only  with  the 
microscope.  The  naturalist  Lebert  affirmed  that 
they  might  always  be  detected  in  diseased  silkworms. 
Dr.  Osimo,  of  Padua,  had  even  perceived  corpuscles 
in  some  of  the  silkworms'  eggs,  and  Dr.  Vittadini  had 
proposed  to  examine  the  eggs  with  a  microscope  in 
order  to  secure  having  sound  ones.  M.  de  Quatre- 
fages only  mentioned  this  matter  of  the  corpuscles  as 


136  LOUIS   PASTEUR. 

a  passing  remark,  being  doubtful  of  its  importance, 
and  perhaps  of  its  accuracy.  This  doubt  might  have 
removed  from  Pasteur's  mind  the  thought  of  examining 
the  significance  of  these  little  corpuscles,  but,  amid  the 
general  confusion  of  opinions,  Pasteur  was  attracted  to 
the  study  of  these  little  bodies  all  the  more  readily 
because  it  related  to  an  organic  element  which  was 
visible  only  with  the  microscope.  This  instrument 
had  already  rendered  such  services  to  Pasteur  in  his 
delicate  experiments  on  ferments,  that  he  was  fasci- 
nated by  the  thought  of  resuming  it  again  as  a  means 
of  research. 


On  June  6,  1865,  Pasteur  started  for  Alais.  The 
emotion  he  felt  on  the  actual  spot  where  the  plague 
raged  in  all  its  force,  in  the  presence  of  a  problem 
requiring  solution,  caused  him  at  once  to  forget  the 
sacrifices  he  had  made  in  quitting  his  laboratory  at 
the  Ecole  Normale.  He  determined  not  to  return  to 
Paris  until  he  had  exhausted  all  the  subjects  requiring 
study,  and  had  triumphed  over  the  plague. 

In  a  few  hours  after  his  arrival  he  had  already 
proved  the  presence  of  corpuscles  in  certain  worms, 
and  was  able  to  show  them  to  the  President  and 
several  members  of  the  Agricultural  Committee,  who 
had  never  seen  them.  The  following  day  he  installed 


THE  SILKWORM-DISEASE.  137 

himself  in  a  little  house  three  kilometers  from  Alais. 
Two  small  cultures  were  there  going  on  ;  they  were 
nearly  the  last,  the  cocoons  had  all  been  spun.  One 
of  these  cultures,  proceeding  from  eggs  imported  that 
very  year  from  Japan,  had  succeeded  very  well.  The 
other,  proceeding  also  from  Japanese  eggs  which  had 
been  reproduced  in  the  country,  had  arrived  at  their 
fourth  moulting  and  had  a  very  bad  appearance. 
But,  strange  to  say,  on. examining  with  the  microscope 
a  number  of  chrysalides  and  moths  of  the  group  which 
had  so  delighted  its  proprietor,  Pasteur  found  cor- 
puscles almost  always  present,  whereas  the  examina- 
tion of  the  worms  of  the  bad  group  only  exhibited 
them  occasionally.  This  double  result  struck  Pasteur 
as  very  strange.  He  at  once  sent  messengers  into  all 
the  neighbourhood  of  Alais  to  seek  for  the  remains  of 
backward  cultivations.  He  attached  extreme  impor- 
tance to  ascertaining  whether  the  presence  of  corpus- 
cles in  the  chrysalides  or  moths  of  the  good  groups,  and 
the  absence  of  the  same  corpuscles  in  the  worms  of  the 
bad  groups,  was  an  accidental  or  a  general  fact.  He 
soon  recognised  that  these  results  did  very  frequently 
occur.  But  what  would  happen  when  the  worms  of 
the  bad  group  spun  their  cocoons?  Pasteur  found 
that  in  the  chrysalides,  especially  in  the  old  ones,  the 
corpuscles  were  numerous.  As  regards  the  moths 
proceeding  from  these  cocoons,  not  one  was  free  from 
them,  and  they  existed  in  profusion. 


138  LOUIS  PASTEUR. 

Following  up  the  idea  that  a  connection  between 
the  disease  and  the  corpuscles  might  possibly  exist, 
as  other  observers  had  previously  imagined,  Pasteur 
declared,  in  a  Note  presented  to  the  Agricultural 
Committee  of  Alais  on  June  26,  1865,  twenty  days 
after  his  arrival,  that  it  was  a  mistake  to  seek  for  the 
corpuscle  in  the  eggs  or  in  the  worms.  Both  the  one 
and  the  other  could  carry  in  them  the  germ  of  the 
disease,  without  exhibiting  distinct  corpuscles,  visible 
under  the  microscope.  The  evil  developed  itself  espe- 
cially in  the  chrysalides  and  in  the  moths,  and  it  was 
in  them  that  search  should  be  made.  Finally,  Pasteur 
came  to  the  conclusion  that  the  only  infallible  method 
of  procuring  healthy  eggs  must  be  by  having  recourse 
to  moths  free  from  corpuscles. 

Pasteur  hastened  to  apply  this  new  method  of  ob- 
taining pure  eggs.  Notwithstanding  that  the  malady 
was  universally  prevalent,  he  succeeded,  after  several 
days  of  assiduous  microscopic  observations,  in  finding 
some  moths  free  from  corpuscles.  He  caretully  pre- 
served their  eggs,  as  well  as  other  eggs  which  had 
proceeded  from  very  corpusculous  couples,  intending  to 
wait  for  what  these  eggs  would  produce  the  following 
year ;  the  first  would  be  probably  free  from  corpuscles, 
while  the  latter  would  contain  them.  He  would  thus 
have  in  future,  though  on  a  small  scale,  samples  of 
originally  healthy  and  of  originally  unhealthy  cultiva- 
tions, by  the  comparison  of  which  with  the  cultivations 


THE  SILKWORM-DISEASE.  139 

of  the  trade — all  more  or  less  smitten  with  the  evil— 
totally  new  views  might  be  expected  to  emerge.  Who 
can  tell,  thought  Pasteur,  whether  the  prosperity  of 
the  silk  cultivation  may  not  depend  on  the  practical 
application  of  this  production  of  pure  eggs  by  means 
of  moths  free  from  corpuscles  ? 

Scarcely  had  Pasteur  made  known,  first  to  the 
Committee  of  Alais,  and  then  to  the  Academy  of 
Sciences,  the  results  of  his  earliest  observations  and 
the  inductions  to  which  they  pointed,  when  critics 
without  number  arose  on  all  sides.  It  was  objected 
that  the  labours  of  several  Italian  savants  had 
established  beyond  all  doubt  that  the  corpuscles  were 
a  normal  element  of  certain  worms,  and  especially  of 
all  the  moths  when  old;  that  other  authors  had 
affirmed  it  to  be  sufficient  to  starve  certain  worms  to 
make  these  famous  corpuscles  appear  in  all  their 
tissues ;  and  that  Dr.  Gaetano  Cantoni  had  already 
tried  some  cultivations  with  eggs  coming  from  moths 
without  corpuscles,  and  that  he  had  totally  failed. 

'  Your  efforts  will  be  vain,'  wrote  the  celebrated 
Italian  entomologist  Cornalia ;  '  your  selected  eggs  will 
produce  healthy  worms,  but  these  worms  will  become 
sickly  through  the  influence  of  the  epidemic  demon 
which  reigns  everywhere.' 

Anyone  but  Pasteur  would  have  been  staggered, 
but  he  was  not  the  man  to  allow  himself  to  be  dis- 


140  LOUIS  PASTEUR. 

couraged  by  a  priori  opinions,  and  by  assertions  which 
were  more  or  less  guesswork.  He  was  resolved  not  to 
abandon  his  preconceived  idea  until  experiment  had 
pronounced  upon  it  with  precision.  All  scientific  re- 
search, in  order  to  be  undertaken  and  followed  up 
with  success,  should  have,  as  point  of  departure,  a 
preconceived  idea,  an  hypothesis  which  we  must  seek 
to  verify  by  experiment.  To  judge  of  the  value  of 
the  facts  which  Pasteur  had  just  announced,  it  was 
necessary  to  know  if  there  existed  the  relation  of  cause 
and  effect  between  the  corpuscles  and  the  disease. 
This  was  the  great  point  to  be  elucidated. 

But  if,  without  preliminary  groping,  he  had  dis- 
covered the  way  to  be  pursued,  Pasteur  subsequently 
brought  to  bear  his  rare  prudence  as  an  experimen- 
talist. For  five  years  he  returned  annually  for  some 
months  to  Alais.  The  little  house  nestling  among 
the  trees  called  Pont-Guisquet  became  at  the  same 
time  his  habitation  and  his  silkworm  nursery.  It  is 
hemmed  in  by  mountains,  up  the  sides  of  which  ter- 
races rise,  one  above  the  other,  planted  with  mulberry 
trees.  The  solitude  was  profound.  Madame  Pasteur 
and  her  daughter  constituted  themselves  silkworm- 
rearers — performing  their  part  in  earnest,  not  only 
gathering  the  leaves  of  the  mulberry  trees,  but  also 
taking  part  in  all  the  experiments.  The  assistants 
of  the  ficole  Normale,  Duclaux,  Maillot,  Gernez, 


THE  SILKWORM-DISEASE.  141 

and  Raulin,  grouped  themselves  around  their  master. 
Thus,  in  an  out-of-the-way  corner  of  the  Cevennes 
was  formed  a  colony  seeking  with  ardour  the  solution 
of  an  obscure  problem,  and  the  means  of  curing  or 
preventing  a  disease  which  had  for  so  long  a  time 
blighted  one  of  the  great  sources  of  the  national 
wealth. 

One  of  the  first  cares  of  Pasteur  was  to  settle  the 
question  as  to  the  contagion  of  the  disease.  Many 
hypotheses  had  been  formed  regarding  this  contagion, 
but  few  experiments  had  been  made,  and  none  of 
them  were  decisive.  Opinions  were  also  very  much 
divided.  Some  considered  that  contagion  was  cer- 
tain ;  the  majority,  however,  either  doubted  or  denied 
its  existence  ;  some  considered  it  as  accidental.  It  was 
said,  for  example,  that  the  evil  was  not  contagious  by 
itself,  but  that  it  became  so  through  the  presence  and 
complication  of  other  diseases  which  were  themselves 
contagions.  This  hypothesis  was  convenient,  and  it 
enabled  contradictory  facts  to  be  explained.  If  some 
persons  had  seen  healthy  worms,  which  had  been 
mixed  up  either  by  mistake  or  intention  with  sickly 
ones,  perish,  and  if  they  insisted  on  contagion, 
others  forthwith  replied  by  diametrically  opposite 
observations. 

But  whatever  the  divergences  of  opinion  might 
be,  everyone  at  all  events  believed  in  the  existence  of 
a  poisonous  medium  rendered  epidemic  by  some  occult 


142  LOUIS  PASTEUR. 

influence.  Pasteur  soon  succeeded,  by  accurate  ex- 
periments, in  proving  absolutely  that  the  evil  was 
contagious. 

One  of  the  first  experiments  was  as  follows.  After 
their  first  moulting,  he  took  some  very  sound  worms 
free  from  corpuscles,  and  fed  them  with  corpusculous 
matter,  which  he  prepared  hi  the  following  simple 
manner.  He  pounded  up  a  silkworm  in  a  little  water, 
and  passed  a  paint-brush  dipped  in  this  liquid  over 
the  whole  surface  of  the  leaves.  During  several  days 
there  was  not  the  least  appearance  of  disease  in  the 
worms  fed  on  those  leaves ;  they  reached  their  second 
moulting  at  the  same  time  as  the  standard  worms 
which  had  not  been  infected.  The  second  moulting 
was  accomplished  without  any  drawback.  This  was 
a  proof  that  all  the  worms,  those  infected  as  well  as 
the  standard  lot,  had  taken  the  same  amount  of 
nourishment.  The  parasite  was  apparently  not  pre- 
sent. Matters  remained  in  this  state  for  some  days 
longer.  Even  the  third  moulting  was  got  through 
without  any  marked  difference  between  the  two  groups 
of  worms.  But  soon  important  changes  set  in.  The 
corpuscles,  which  had  hitherto  only  showed  themselves 
in  the  integuments  of  the  intestines,  began  to  appear 
in  the  other  organs.  From  the  second  day  follow- 
ing the  third  moulting — that  is  to  say,  the  twelfth 
after  the  infection — a  visible  inequality  distinguished 
the  infected  from  the  non-infected  worms.  Those 


THE  SILKWORM-DISEASE.  143 

of  the  standard  lot  were  clearly  in  much  the  best 
health.  On  examining  the  infected  worms  through 
a  magnifying  glass,  a  multitude  of  little  spots  were 
discovered  on  their  heads,  and  on  the  rings  of  their 
bodies,  which  had  not  before  shown  themselves.  These 
spots  appeared  on  the  exterior  skin  when  the  interior 
skin  of  the  intestinal  canal  contained  a  considerable 
number  of  corpuscles.  It  was  these  corpuscles  that 
impeded  the  digestive  functions,  and  interfered  with 
the  assimilation  of  the  food.  Hence  arose  the  in- 
equality of  size  of  the  worms.  After  the  fourth  moult- 
ing, the  same  type  of  disease  was  noticed  a»s  that 
which  was  breaking  out  everywhere  in  the  silkworm 
nurseries,  especially  the  symptom  of  spots  on  the 
skin,  which  had  led  to  the  disease  being  called  pebrine. 
The  peasants  said  that  the  worms  were  peppered. 
The  majority  of  the  worms  were  full  of  corpuscles. 
Those  which  spun  their  cocoons  produced  chrysalides 
which  were  nothing  but  corpusculous  pulp,  if  such 
a  term  be  allowed. 

It  was  thus  proved  that  the  corpuscles,  introduced 
into  the  intestinal  canal  at  the  same  time  as  the  food 
of  the  worms,  convey  the  infection  into  the  intestinal 
canal,  and  progressively  into  all  the  tissues.  The 
malady  had  in  certain  cases  a  long  period  of  incuba- 
tion, since  it  was  only  on  the  twelfth  day  that  it  be- 
came perceptible.  Finally,  the  spots  of  pebrine  on 
the  skin,  far  from  being  the  disease  itself,  were  but 


144  LOUIS  PASTEUR. 

the  effect  of  the  corpuscles  developed  in  the  interior  ; 
they  were  but  a  sign,  already  removed  from  the  true 
seat  of  the  evil.  '  If  these  spots  of  pebrine,'  thought 
Pasteur,  '  were  considered  in  conjunction  with  certain 
human  maladies  in  which  spots  and  irruptions  appear 
on  the  body,  what  interesting  inductions  might  pre- 
sent themselves  to  minds  prepared  to  receive  them ! ' 

Pasteur  was  never  tired  of  repeating  this  curious 
experiment,  or  of  varying  its  conditions.  Sometimes 
he  introduced  the  corpusculous  food  into  healthy 
worms  at  their  birth,  sometimes  at  the  second  or 
third  moulting.  Occasionally,  when  the  worms  were 
about  to  spin  their  cocoons,  the  corpusculous  food  was 
given  them.  All  the  disasters  that  were  known  to 
have  happened  in  the  silkworm  nurseries,  their  extent 
and  their  varied  forms,  were  faithfully  reproduced. 
Pasteur  created  at  will  any  required  manifestation  of. 
pebrine.  When  he  infected  quite  healthy  worms,  after 
their  fourth  moulting,  with  fresh  corpusculous  matter, 
these  worms,  even  after  several  meals  of  corpusculous 
leaves  alternated  with  meals  of  wholesome  leaves, 
made  their  cocoons.  It  might  have  been  supposed 
that  in  this  case  the  contagion  had  not  taken  effect. 
This  was  but  a  deceptive  appearance.  The  communi- 
cation of  the  disease  exhibited  itself  in  a  marked  de- 
gree in  the  chrysalides  and  in  the  moths.  Many  of 
the  chrysalides  died  before  they  turned  into  moths, 
and  their  bodies  might  be  said  to  be  entirely  composed 


THE   SILKWORM-DISEASE.  145 

of  corpuscles.  Such  moths  as  were  formed,  and  which 
emerged  from  their  cocoons,  had  a  most  miserable  ap- 
pearance. The  disease  sometimes  went  so  far  as  to 
render  breeding  and  the  laying  of  eggs  impossible. 

Faithful  to  the  rules  prescribed  by  the  experi- 
mental method,  Pasteur  was  careful  to  reproduce 
these  same  experiments  with  the  worms  of  the 
standard  lot,  from  which  all  infected  worms  had 
been  selected.  He  fed  these  healthy  wrorms  on  leaves 
over  which  a  clear  infusion  made  from  the  remains  of 
moths  or  worms  exempt  from  corpuscles  had  been 
spread  with  a  paint-brush,  instead  of  leaves  conta- 
minated with  corpusculous  remains.  This  food  kept 
the  worms  in  their  usual  health.  Could  there  be  a 
better  proof  that  the  corpuscles  alone  were  the  real 
cause  of  the  pebrine  disease  ? 

These  experiments,  I  repeat,  threw  a  strong  light 
on  the  nature  of  the  disease,  and  exactly  accounted 
for  what  took  place  in  the  industrial  cultivations. 
From  the  malady  which  attacked  the  worms  at  their 
birth,  decimating  a  whole  cultivation,  dowrn  to  the 
invisible  disease  that  may  be  said  to  inclose  itself 
in  the  cocoon,  all  was  now  explained.  One  of  the 
effects  of  the  plague  which  had  most  excited  the  sur- 
prise and  thwarted  the  efforts  of  cultivators  was  the 
impossibility  of  finding  productive  eggs,  even  when 
they  tried  to  obtain  them  from  the  cocoons  of  groups 
which  had  succeeded  perfectly  well  as  far  as  the  pro- 


146  LOUIS  PASTEUE. 

duction  of  cocoons  was  concerned.  It  was  proved 
that  almost  invariably  the  following  year  the  eggs  of 
these  fine-looking  groups  were  unproductive.  Num- 
bers of  the  agricultural  boards,  and  practitioners,  not 
being  able  to  believe  in  the  existence  of  the  disease  in 
collections  that  were  so  satisfactory  as  regards  the 
abundance  and  beauty  of  the  cocoons,  persisted  in 
thinking  that  the  failures  had  an  origin  not  connected 
with  the  seed  itself.  This  resulted  in  deception  after 
deception,  often  even  in  mistakes  that  were  much  to 
be  regretted.  Frequently  the  best  husbandmen  were 
known  to  reserve  for  the  production  of  eggs  some 
very  fine  cultivations,  not  having  observed  in  the 
worms  either  spots  of  pebrine  or  corpuscles  even  up 
to  the  time  when  the  mounting  of  the  brambles  had 
been  accomplished;  and  the  year  following  they  had 
the  pain  of  seeing  all  the  cultivations  from  these  eggs 
perish.  These  circumstances,  so  well  calculated  to 
produce  discouragement  and  to  give  the  disease  a 
mysterious  character,  met  with  their  natural  explana- 
tion in  the  facts  proved  by  experimental  infection. 

Still,  as  it  never  occurs  to  the  cultivator  to  infect 
the  worms  directly  by  giving  them  food  charged  with 
corpusculous  debris,  it  might  be  asked  how,  in  the 
industrial  establishments,  such  results  can  be  pro- 
duced. Pasteur  lost  no  time  in  solving  this  difficulty. 

In  a  cultivation  containing  corpusculous  worms 
these  worms  perpetually  furnish  contagious  matter, 


THE  SILKWORM-DISEASE.  147 

which  falls  upon  the  leaf  and  fouls  it.  This  is  the 
excreta  of  the  worms,  which  the  microscope  shows  to 
be  more  or  less  filled  with  corpuscles  drawn  from  the 
lining  of  the  intestinal  canal.  It  is  there  that  they 
swarm.  It  is  easy  to  understand  that  these  excreta, 
falling  on  the  leaves,  contaminate  them  all  the  more 
easily  because  the  worms,  by  the  weight  of  their  bodies 
in  crawling,  press  the  excreta  against  the  leaves. 
This  is  one  cause  of  natural  contagion.  By  the  ex- 
creta of  corpusculous  worms  which  he  crushed,  mixed 
with  water,  and  spread  with  a  paint-brush  over  the 
mulberry  leaves  intended  for  a  single  meal,  Pasteur 
was  able  to  communicate  the  contagion  to  as  many 
worms  as  he  liked. 

He  also  indicated  another  natural  and  direct  cause 
of  contagion.  The  six  fore-feet  of  the  worm  have 
sharp  hooks  at  their  ends,  by  means  of  which  the 
worms  prick  each  other's  skins.  Let  any  one  imagine 
a  healthy  worm  passing  over  the  body  of  the  corpus- 
culous worm.  The  hooks  of  the  first  worm,  by  pene- 
trating the  skin  of  the  second,  are  liable  to  be  soiled 
by  the  corpuscles  immediately  below  that  skin ;  and 
these  hooks  are  capable  of  carrying  the  seeds  of  dis- 
ease to  other  healthy  worms,  which  may  be  pricked  in 
their  turn.  To  demonstrate  experimentally,  as  Pas- 
teur did,  the  existence  of  this  cause  of  contagion,  it 
was  only  necessary  to  take  some  worms  and  allow 
them  to  wound  each  other.  Lastly,  infection  at  a 


148  LOUIS  PASTEUR. 

distance,  through  the  medium  of  the  air  and  the  dust  it 
carries,  is  a  fact  equally  well  established.  It  is  suffi- 
cient, by  sweeping  the  breeding-houses,  or  by  shaking 
the  hurdles,  to  stir  up  the  dust  of  corpusculous  excre- 
tions and  the  dried  remains  of  dead  worms,  and  to 
allow  them  to  be  spread  over  the  hurdles  of  the 
healthy  worms,  to  cause,  after  a  certain  time,  con- 
tagion to  appear  among  these  worms.  When  very 
healthy  worms  were  placed  in  a  breeding  nursery  at  a 
considerable  distance  from  unhealthy  worms,  they,  in 
their  turn,  became  infected. 

After  so  many  decisive  experiments  it  was  no 
longer  possible  not  to  see  in  pebrine  an  essentially 
contagious  disease.  Nevertheless,  among  facts  in- 
voked in  favour  of  non-contagion,  there  was  one  which 
it  was  difficult  to  explain.  There  existed  several 
examples  of  successful  cultivations  conducted  in 
nurseries  which  had  totally  failed  from  the  effects  of 
pebrine  the  year  before.  The  explanation  is,  as  shown 
by  Pasteur,  that  the  dust  can  only  act  as  a  con- 
tagion when  it  is  fresh.  Corpusculous  matter,  when 
thoroughly  dried,  loses  its  virulence.  A  few  weeks 
suffice  to  render  such  matter  inoffensive :  hence  the 
dust  of  one  year  is  not  injurious  to  the  cultivations  of 
the  next  year.  The  corpuscles  contained  in  the  eggs 
intended  for  future  cultivation  alone  cause  the  trans- 
mission of  the  disease  to  future  generations. 

And  what  can  be  more  easily  understood  than  the 


THE  SILKWOEM-DISEASE.  149 

presence  of  corpusculous  parasites  in  the  egg  ?  The 
egg  comes  into  existence  during  that  marvellous  phase 
of  the  life  of  a  silkworm  when,  after  having  spun  its 
cocoon,  it  sleeps  within  it  as  a  chrysalis,  resolving  itself, 
so  to  speak,  into  those  kinds  of  albumen  and  yelk 
from  which  the  fully-formed  moth  will  emerge,  as  a 
chick  emerges  from  its  egg.  Let  anyone  imagine 
this  origin  of  an  approaching  life,  no  longer  in  its 
normal  purity,  but  associated  with  a  parasite  which 
will  find  in  the  materials  surrounding  it,  so  adapted 
to  life  and  transformation,  the  elements  of  its  own 
nourishment  and  multiplication.  This  parasite  will  be 
present  when  the  eggs  of  the  female  moth,  tender  and 
soft  as  albumen,  begin  to  define  their  outlines.  Woe 
betide  those  eggs  if  they  then  enclose  any  particles  of 
corpuscle,  or  of  its  original  matrix.  In  vain  will  the 
envelope  of  those  eggs  become  by  degrees  hard  and 
horny ;  the  enemy  is  within,  and  later  on  he  will  be 
discovered  in  the  embryo  of  the  silkworm. 

Thus  this  terrible  plague  is  at  the  same  time  con- 
tagious and  hereditary,  helping  us  to  understand  the 
evolution  of  this  double  character  in  certain  maladies 
both  of  men  and  animals. 

II. 

The  first  time  Pasteur  went  to  Alais  the  silkworm 
epidemic  was  universally  attributed  to  a  single  cause 
— pebrine.  Pebrine  was  called  the  disease.  This 


150  LOUIS  PASTEUR. 

word  expressed  everything.  It  indicated  the  existence 
of  a  mysterious  scourge,  the  origin  and  nature  of 
which  could  not  be  traced,  but  which  was  ready  to 
fall  upon  all  the  establishments  devoted  to  the  nurture 
of  the  worms.  Whatever  might  happen,  or  whatever 
might  be  the  cause  of  ruin  in  a  silkworm  nursery,  the 
disease  was  held  responsible.  One  of  the  most  striking 
proofs  that  the  evil  was  attributed  to  pebrine  alone  is 
found  in  the  fact  that  a  prize  of  5,000  florins  was 
offered  by  the  Austrian  Government  in  1868,  as  a 
reward  for  the  discovery  of  the  best  remedy  for  the 
prevention  and  cure  of  pebrine — '  the  epidemic  disease 
which  devastates  the  silkworm.' 

A  rapid  glance  at  the  principles  which  have  just 
been  established  suffices  to  show  that  pebrine  might 
now  be  regarded  as  vanquished.  Pasteur  had  de- 
monstrated that  moths  free  from  corpuscles  never 
produced  a  single  corpusculous  egg ;  he  had  proved, 
moreover,  that  eggs  brought  up  in  a  state  of  isolation, 
at  a  distance  from  contaminated  eggs,  produce  no 
worms,  chrysalides,  or  moths  which  are  corpusculous. 
It  was  easy,  therefore,  to  multiply  cultivations  free  from 
pebrine.  The  production  of  silk  and  the  production  of 
eggs  was  thus  secured.  To  make  sure  that  the  eggs 
were  pure  it  was  only  necessary  to  have  recourse  to 
the  microscopic  examination  of  the  moths  which  had 
produced  them.  These  observations  might  be  made 
by  women,  by  young  girls,  even  by  children.  It  was 


THE  SILKWORM-DISEASE.  151 

sufficient  to  crush  up  a  moth  in  a  little  water,  and  to 
put  a  drop  of  this  mixture  under  the  microscope,  to 
see  the  corpuscles  clearly,  if  they  existed.  It  seemed, 
then,  that  the  plague  was  got  rid  of.  But  Pasteur  was 
not  slow  in  recognising  that  the  general  belief  in  a 
single  malady  could  not  be  justified.  If  the  experi- 
ments of  1866  had  demonstrated  to  him  the  full  ex- 
tent of  the  corpusculous  malady,  and  had  established 
the  principles  of  a  treatment  proper  for  its  prevention, 
the  method  he  had  adopted  had  also  shown  him  that 
pebrine  was  far  from  being  the  only  cause  from  which 
the  silk  culture  suffered. 

It  was  in  1867  that  this  result  was  obtained. 
From  an  experimental  point  of  view,  that  year  counted 
double  for  Pasteur.  Influenced  by  a  profound  sym- 
pathy for  the  misery  which  he  had  witnessed  during 
two  successive  years,  and,  at  the  same  time,  impatient 
to  find  the  cause  of  the  scourge,  Pasteur,  in  the 
months  of  February,  March,  and  April,  in  advance  of 
the  great  industrial  cultivations,  commenced  a  series 
of  experiments  on  worms  hatched  by  artificial  heat, 
and  fed  with  mulberry  leaves  from  a  hothouse. 

During  these  forced  experiments  Pasteur  observed 
that  out  of  sixteen  broods  derived  from  non-corpus- 
culous  parents,  fifteen  succeeded,  while  the  sixteenth 
perished  almost  entirely  between  the  fourth  moulting 
and  the  climbing  on  to  the  brambles.  After  having 
exhibited  a  most  healthful  appearance,  the  worms  died 
9 


152  LOUIS  PASTEUE. 

suddenly.  In  a  cultivation  of  100  worms,  ten,  fifteen, 
twenty  dead  ones  were  picked  up  daily :  these  turned 
black,  and  became  putrid  with  extraordinary  rapidity, 
often  within  the  space  of  twenty-four  hours.  Some- 
times they  were  soft  and  flabby,  like  an  empty, 
crumpled  intestine.  Consulting  the  authors  who  had 
written  upon  silkworms,  Pasteur  could  not  doubt  that 
he  had  before  his  eyes  a  characteristic  specimen  of  the 
disease  called  morts-flats,  or  flacherie.  Not  only  were 
these  worms  free  from  all  pebrine  spots,  but  no  cor- 
puscles were  to  be  found  in  any  part  of  their  bodies. 
A  still  more  significant  fact  was,  that  corpuscles  were 
also  absent  from  the  chrysalides  and  the  moths  of 
those  few  worms  which  were  able  to  spin  their  cocoons. 
Although  this  sample  was  confined  to  a  single  group 
of  eggs  derived  from  parents  free  from  corpuscles, 
Pasteur  continued  to  entertain  doubts  as  to  the  exist- 
ence of  only  a  single  disease,  and  also  as  to  the  neces- 
sary connection  of  pebrine  with  flacherie. 

These  suspicions  were  confirmed  by  his  cultiva- 
tions of  April  and  May.  Numerous  cases  of  flacherie 
presented  themselves.  Uncertainty  was  no  longer 
possible  as  to  the  mutual  independence  of  the  two 
maladies — pebrine  and  flacherie.  The  cultivations 
most  seriously  invaded  by  the  last-mentioned  disease 
came  from  eggs  produced  by  parents  free  from  cor- 
puscles, and  led  on  to  reproducers  also  free  from  this 
parasite.  On  visiting  a  multitude  of  industrial  cultiva- 


THE  SILKWOKM-DISEASE.  153 

tions,  Pasteur  discerned  that  what  had  passed  in  his 
own  laboratory  was  of  very  general  occurrence,  and 
that,  contrary  to  the  received  opinion,  two  distinct 
maladies  divided  between  them  the  cause  of  all  the 
misfortunes.  Pebrine  was  evidently  the  most  widely 
spread,  but  flacherie  had  also  its  share,  and  a  very 
large  share,  in  the  calamity. 

Here,  once  more,  the  microscope  came  to  Pasteur's 
assistance.  If,  at  the  period  of  the  rearing  of  the 
silkworms,  when  the  mean  temperature  is  always 
rather  high,  some  mulberry  leaves  are  crushed  in  a 
mortar  and  mixed  with  a  little  water,  the  liquid  being 
left  to  itself,  in  twenty-four  hours  it  will  be  found 
filled  with  microscopic  organisms;  some  motionless, 
resembling  little  rods  or  spores'  joined  end  to  end, 
like  strings  of  beads,  others  more  or  less  active, 
flexible,  endowed  with  a  sinuous  movement  like  that 
of  the  vibrios  found  in  nearly  all  organic  infusions  in 
process  of  decomposition.  Whence  come  these  micro- 
scopic organisms  ?  The  facts  relating  to  spontaneous 
generation  indicate  that  the  germs  of  these  organisms 
were  on  the  surface  of  the  pounded  leaf,  spread  in  the 
form  of  dust  over  the  instruments  used  to  triturate 
the  leaf,  possibly  on  the  mortar,  the  pestle,  or  in  the 
water  added  to  the  pounded  leaves. 

It  is  a  curious  fact,  that  if  the  intestinal  canal  of 
a  worm  in  full  process  of  digestion  be  opened,  the 
pounded  leaf  which  fills  it  from  one  end  to  the  other 


154  LOUIS  PASTEUR. 

will  not  show  microscopic  organisms  of  any  kind, 
but  only  cells  of  parenchyma,  green  granules  of  the 
chlorophyl  of  the  leaf,  and  remains  of  the  air-vessels 
of  the  plant.  Through  the  action  of  the  liquids 
secreted  by  the  glands  which  line  the  integuments  of 
the  intestinal  canal,  the  germs  of  organisms  are  them- 
selves digested  or  hindered  hi  their  development.  The 
digestive  functions  of  silkworms  are  so  active  that 
everything  is  carried  away,  destroyed  in  the  same 
manner  as  the  leaves  themselves. 

But  if  from  any  cause  the  digestion  of  the  worms 
be  impeded  or  suspended,  then  the  germs  introduced 
with  the  food  into  the  intestinal  canal  will  give  rise 
to  the  multiplication  of  microscopic  organisms  which 
are  always  found  in  the  artificially  bruised  leaf  when 
mixed  with  a  little  water.  How  numerous  are  the 
causes  which  may  check  this  digestive  function  of  the 
worm — a  function  of  such  importance  to  a  creature 
which  in  the  space  of  one  month  passes  from  the 
weight  of  half  a  milligramme  to  that  of  five,  six,  seven, 
or  even  eight  grammes  !  Pasteur  proved  that  when- 
ever a  worm  was  attacked  with  flacherie,  it  always  had, 
associated  with  the  food  in  its  intestinal  canal,  one  or 
other  of  the  microscopic  organisms  which  are  in- 
variably to  be  met  with  among  crushed  mulberry  leaves. 
Summing  up  in  a  kind  of  aphorism  a  series  of  ob- 
servations, Pasteur  observes  :  '  Every  ver  flat  is  one 
which  digests  badly,  and,  conversely,  every  worm 


THE  SILKWORM-DISEASE.  155 

which  digests  badly  is  doomed  to  perish  of  flacherie, 
or  to  furnish  a  chrysalis  and  a  moth  the  life  of  which, 
through  ths  injury  produced  by  organised  ferments, 
is  not  normally  perfected.' 

Thus,  as  in  the  case  of  pebrine,  the  morbid  sym- 
ptoms of  flacherie  are  very  variable.  All  depends  on 
the  intensity  of  the  evil — that  is  to  say,  on  the  abun- 
dance and  the  nature  of  the  parasites  developed  in  the 
intestinal  canal,  and  also  on  the  period  in  the  life  of 
the  worm  when  this  fermentation  begins  to  show  itself. 
The  most  dangerous  of  all  these  ferments  are  those  of 
the  family  of  vibrios.  If  they  exist  in  the  first  phases 
of  the  life  of  the  worm,  it  dies  quickly  and  very  soon 
becomes  putrid,  sometimes  resolving  itself  into  an  in- 
fected pus.  The  disease  often  manifests  itself  in  a 
manner  particularly  distressing  and  disastrous  to  the 
cultivator.  The  worms  have  presented  the  most  beau- 
tiful appearance  up  to  the  time  of  climbing  the 
heather.  The  mortality  has  scarcely  been  two  or 
three  per  cent.,  which  is  nothing;  the  moultings  have 
been  effected  in  a  perfect  manner,  when  suddenly, 
some  days  after  the  fourth  moulting,  the  worms  be- 
come languid,  crawling  with  difficulty,  and  hesitating 
to  take  the  leaves  which  are  thrown  upon  their 
hurdles.  If  some  few  have  mounted  on  to  the  heather, 
they  stretch  themselves  on  the  twigs,  their  bodies  swollen 
with  food  which  they  cannot  digest.  Sometimes  they 
remain  there  motionless  till  they  die,  or,  falling,  remain 


156  LOUIS  PASTEUK. 

suspended  only  by  their  false  feet.  The  few  moths  which 
have  succeeded  in  piercing  their  cocoons  do  not  show 
any  corpuscles.  They  can  produce  eggs,  but  these 
eggs,  coming  from  parents  weakened  by  disease,  give 
rise  the  following  year  to  a  generation  threatened 
with  flacherie.  It  is  in  this  sense  that  the  disease 
may  be  regarded  as  hereditary,  although  the  para- 
sites of  the  intestinal  canal  to  which  flacherie  is  due 
do  not  transmit  themselves  to  the  eggs  or  to  the 
worms  which  issue  from  them.  The  worms  inherit 
weakly  constitutions,  and,  being  without  power  of 
resistance  against  anything  that  can  derange  their 
digestive  functions,  they  are  at  the  mercy  of  the 
accidents  of  their  culture. 

Too  large  an  assemblage  of  worms  in  one  nursery  ; 
too  high  a  temperature  at  the  time  of  moulting;  a 
thunderous  atmosphere,  which  predisposes  organic 
matter  to  fermentation ;  the  use  of  heated  or  wet 
leaves,  especially  if  the  wetting  be  caused  by  a  fog  or 
by  the  morning  or  evening  dew,  which  deposits  on  the 
leaf  the  germs  suspended  in  a  great  mass  of  air ; — these 
are  so  many  causes  calculated  to  diminish  the  activity 
of  the  digestive  functions  of  the  worms,  and  to  produce 
in  consequence  a  fermentation  of  the  leaf  in  the  in- 
testinal canal — the  malady  now  under  consideration. 
Often  also  flacherie  depends  upon  mistakes  committed 
by  the  husbandman  while  tending  his  precious  '  kine,' 
to  use  an  expression  of  the  sixteenth  century. 


THE  SILKWORM-DISEASE.  157 

A  Chinese  book  published  on  the  rearing  of  silk- 
worms contains  a  series  of  little  practical  counsels. 
'  The  person  who  takes  care  of  the  silkworms,'  says 
this  guide  to  the  perfect  cultivator,  '  ought  to  wear  a 
simple  garment,  not  lined.  He  must  regulate  the 
temperature  of  the  spinning-house  according  to  the 
sensation  of  heat  or  cold  which  he  experiences ;  if  he 
feels  cold,  he  may  conclude  that  the  worms  are  cold, 
and  he  will  increase  the  fire ;  if  he  feels  hot,  he  will 
conclude  that  the  worms  are  hot,  and  he  will  suitably 
dimmish  the  fire.' 

One  point  which  had  been  ignored  before  the  ex- 
periments of  Pasteur  was  the  contagious  character  of 
flacherie.  This  contagion  may  surpass  that  of  pcbrine 
itself  as  regards  duration.  In  pebrine  the  dried  cor- 
pusculous  matter  loses  all  virulence  after  the  lapse 
of  some  weeks.  The  disease  cannot,  therefore,  com- 
municate itself  from  one  year  to  another  by  the  cor- 
pusculous  dust  of  a  rearing  establishment.  The  germs, 
on  the  contrary,  of  the  microscopic  organisms  which 
provoke  fermentation  in  the  mulberry  leaves,  especially 
the  vibrios,  retain  their  vitality  for  several  years.  The 
dust  of  a  silkworm  nursery  infected  by  flaclierie  ap- 
pears under  a  microscope  quite  full  of  cysts  or  spores 
of  vibrios.  These  spores  or  cysts  rest,  like  the  sleep- 
ing beauty  in  the  forest,  until  a  drop  of  water  falls 
upon  them  and  awakens  them  into  life.  Deposited 
on  the  leaves  which  are  to  serve  as  nourishment, 


158  LOUIS  PASTEUR. 

these  germs  of  vibrios  are  carried  into  the  intestinal 
canal  of  the  worm,  develop  and  multiply  themselves, 
and  completely  disturb  the  digestive  functions,  unless 
the  digestion  is  so  strong  that  the  germs  are  imme- 
diately arrested,  and  disposed  of  like  the  food  itself. 
This  is  what  happens  when  the  worms  are  in  full 
vigour.  It  is  a  struggle  for  life,  in  which  the  worms 
often  gain  the  victory. 

Giving  to  some  very  healthy  worms  a  meal  of 
leaves  covered  with  the  dry  dust  of  a  silkworm 
nursery,  infected  the  year  before  by  pebrine  and 
flacherie,  Pasteur  reproduced  flacherie,  and  not  pebrine. 
Still  more  readily  did  he  produce  the  first  of  these 
maladies,  when  he  gave,  as  food,  leaves  polluted  by 
the  contents  of  the  intestinal  canal  of  worms  which 
had  died  of  the  disease.  As  in  the  case  of  pebrine, 
the  excreta  of  the  worms  attacked  by  flacherie,  de- 
filing the  leaves,  carry  the  mischief  to  the  healthy 
worms,  or  add  to  the  dangerous  fermentation  in  the 
intestines  of  those  which  are  already  in  part  attacked. 

To  preserve  silkworms  from  accidental  flacherie, 
hygienic  precautions  are  sufficient.  As  regards  here- 
ditary flacherie,  or,  to  speak  more  correctly,  that  which 
develops  itself  easily  on  any  diminution  of  vigour  in 
the  eggs  and  in  the  embryo,  Pasteur  again  found  a 
remedy  by  having  recourse  to  the  microscope.  By 
means  of  the  microscope  it  is  possible  to  obtain  in- 
formation as  to  the  health  of  the  worms,  the  chry- 


THE  SILKWOKM-DISEASE.  159 

salides,  and  the  moths  destined  to  produce  the  eggs. 
Every  attention  should  be  directed  to  the  complete 
exclusion  of  ferments  from  the  intestinal  canal  of  the 
worms,  and  from  the  stomach-pouch  of  the  chrysalides — 
a  little  pouch  to  which  the  intestinal  canal  of  the  worm 
is  reduced,  with  its  contents  more  or  less  transformed. 
But  if  there  is  not  time  to  make  this  examination  for 
parasitic  ferments  with  the  microscope,  a  simple  in- 
spection of  the  worms  in  their  last  stage  will  suffice. 
Pasteur  laid  great  stress  upon  the  observation  of  the 
worms  when  they  climbed  on  to  the  heather. 

'  If  I  were  a  cultivator  of  silkworms,'  he  wrote  in 
his  beautiful  work  on  the  diseases  of  silkworms,  '  I 
would  never  hatch  an  egg  produced  from  worms  that 
I  had  not  observed  many  times  during  the  last  days 
of  their  life,  so  as  to  make  sure  of  their  vigour  at  the 
moment  when  they  spin  their  silk.  If  you  use  eggs 
produced  by  moths  the  worms  of  which  have  mounted 
the  heather  with  agility,  have  shown  no  signs  of 
flacherie  between  the  fourth  moulting  and  mounting 
time,  and  do  not  contain  the  least  corpuscle  of  pebrine, 
then  you  will  succeed  in  all  your  cultivations.' 

ni. 

We  have  now  arrived  at  the  end  of  this  long  in- 
vestigation. All  the  obscurity  which  enveloped  the 
origin  of  the  diseases  of  silkworms  had  now  been  dis- 


160  LOUIS  PASTEUE. 

pelled.  Pasteur  had  arrived  at  such  accurate  know- 
ledge both  of  the  causes  of  the  evil  and  their  different 
manifestations,  that  he  was  able  to  produce  at  will 
either  pebrine  or  flacherie.  He  could  so  regulate  the 
intensity  of  the  disease  as  to  cause  it  to  appear  on  a 
given  day,  almost  at  a  given  hour.  He  had  now  to 
carry  into  practice  the  results  of  his  laboratory 
labours. 

Since  the  beginning  of  the  plague,  and  after  some 
doubts  which  were  soon  dispelled,  it  was  clearly  seen 
that  all  the  mischief  was  to  be  attributed  to  the  bad 
condition  of  the  eggs.  The  remedy  of  distant  explora- 
tions for  procuring  non-infected  eggs  was  both  insuffi- 
cient and  precarious.  It  simply  amounted  to  going 
very  far  to  seek,  and  paying  very  dear,  for  seed 
which  could  not  be  relied  on  with  certainty.  The 
prosperity  of  the  silkworm  culture  could  only  be 
secured  by  measures  capable  of  restoring  to  the  native 
eggs  their  pristine  qualities. 

The  results  obtained  by  Pasteur  were  sufficient  to 
solve  this  problem.  The  struggle  against  flacherie 
was  easy,  but  there  remained  the  struggle  against 
pebrine.  To  triumph  over  this  disease,  which  was  so 
threatening,  Pasteur  devised  a  series  of  observations 
as  simple  as  they  were  ingenious. 

Here  is  a  crop  which  has  perfectly  succeeded.  The 
moultings,  and  the  climbing  upon  the  heather,  are  all 
that  could  be  desired.  The  cocoons  are  finished,  and  the, 


THE  SILKWORM-DISEASE.  161 

appearance  of  the  moths  alone  is  waited  for.  They 
arrive,  and  they  pair.  Then  begins  the  work  of  the 
cultivator,  who  is  careful  about  the  production  of  his 
eggs.  He  separates  the  couples  at  the  end  of  the  day ; 
laying  each  female  moth  by  itself  on  a  little  linen 
cloth  suspended  horizontally.  The  females  lay  their 
eggs.  After  the  laying,  he  takes  each  female  in  turn 
and  secures  her  by  a  pin  passed  through  the  wings  to 
a  folded  corner  of  the  little  cloth,  where  are  grouped 
some  hundreds  of  eggs  which  she  has  laid.  The  male 
moth  also  might  be  pinned  in  another  corner  of 
the  cloth,  but  the  examination  of  the  male  is  useless, 
as  it  has  been  found  that  he  does  not  communicate 
the  pebrine.  The  female  moth,  after  having  been 
desiccated  by  free  contact  with  the  air,  is  examined  at 
leisure,  it  may  be  even  in  the  autumn  or  winter.  No- 
thing is  easier  than  to  ascertain  whether  there  are  any 
corpuscles  in  its  dead  body.  The  moth  is  crushed  in  a 
mortar  and  mixed  with  a  little  water,  and  then  a  drop 
of  the  mixture  is  examined  by  the  microscope.  If 
corpuscles  be  found,  the  bit  of  cloth  corresponding  to 
the  examined  moth  is  known,  and  it  is  burnt  with  all 
the  eggs  it  contains. 

This  method  of  procuring  pure  eggs  is,  in  fact,  only 
the  rational  development  of  the  first  inductions  which 
Pasteur  had  submitted  to  the  Agricultural  Committee 
of  Alais  in  June  1865.  At  that  time  he  hardly  ven- 
tured to  hope  that  he  should  be  able  to  find  the  means 


162  LOUIS  PASTEUR. 

of  preparing  more  than  very  small  quantities  of 
healthy  eggs  for  his  experiments ;  but  events  were 
so  ordered  that  the  starting-point,  which  seemed  to 
be  purely  scientific,  unfolded  a  method  susceptible 
of  a  widespread  practical  application.  This  process 
of  procuring  sound  eggs  is  now  universally  adopted. 
In  the  Basses-Alpes,  in  Ardeche,  in  Gard,  in  the 
Drome,  and  in  other  countries,  may  be  met  with 
everywhere,  at  the  time  of  the  cultivation,  workshops 
where  hundreds  of  women  and  young  girls  are  occu- 
pied, with  a  remarkable  division  of  labour  and  under 
the  strictest  supervision  of  skilful  overseers,  in  pound- 
ing the  moths,  in  examining  them  microscopically, 
and  in  sorting  and  classifying  the  little  cloths  upon 
which  the  eggs  are  deposited. 

But  if  Pasteur  had  brought  back  wealth  to  ruined 
countries,  if  he  had  returned  to  Paris  happy  in  the 
victory  he  had  gained,  he  had  also  undergone  such 
fatigues,  and  had  so  overstrained  himself  in  the  use 
of  the  microscope  while  absorbed  in  his  daily  and 
varied  experiments,  that  in  October  1868  he  was 
struck  with  paralysis  of  one  side.  Seeing,  as  he 
thought,  death  approaching,  he  dictated  to  his  wife  a 
last  note  on  the  studies  which  he  had  so  much  at 
heart.  This  note  was  communicated  to  the  Academy 
of  Sciences  eight  days  after  this  terrible  trial. 

A  soul  like  his,  possessing  so  great  a  mastery  over 


THE  SILKWORM-DISEASE.  163 

the  body,  ended  by  triumphing  over  the  affliction. 
Paralysed  on  the  left  side,  Pasteur  never  recovered  the 
use  of  his  limbs.  To  this  day,  sixteen  years  after  the 
attack,  he  limps  like  a  wounded  man.  But  what 
stages  had  this  wounded  man  yet  to  travel  over,  what 
triumphs  were  yet  in  store  for  him  ! 


164  LOUIS   PASTEUR. 


DECISIVE  EXPERIMENTS. 

AFTER  having  dictated  this  scientific  note,  which  he 
thought  would  have  been  his  last,  his  courage  forsook 
him  for  a  time.  '  I  regret  to  die,'  he  said  to  his 
friend,  Sainte- Claire  Deville,  who  had  hastened  to  his 
bedside ;  '  I  should  have  wished  to  render  more  service 
to  my  country.'  His  life  was  spared,  but  for  several 
months  Pasteur  remained  entirely  paralysed,  incapable 
of  the  slightest  movement.  Smitten  "thus  in  his  full 
strength  at  the  age  of  forty-five,  he  took  a  sad  review 
of  his  own  state.  Even  at  the  height  of  his  attack 
his  mind  had  always  retained  its  clearness.  He  had 
pointed  out  to  the  doctor  without  any  faltering  of 
voice  the  progressive  symptoms  of  the  paralysis.  Then 
reproaching  himself  for  having  added  to  the  grief  of 
his  wife  by  thus  dwelling  on  the  details  of  his  illness, 
he  never  allowed  another  word  to  escape  him  about 
his  infirm  condition.  Sometimes,  even  when  he 
heard  his  two  assistants,  M.  Gernez  and  M.  Duclaux, 
whose  devotion  to  him  during  those  sad  days  could 
only  be  compared  to  that  of  his  wife,  talking  to  him  of 


DECISIVE  EXPERIMENTS.  165 

future  labours,  he  entered  into  these  thoughts  and 
appeared  to  add  faith  to  their  hopes.  He  finished  by 
sharing  them. 

In  January  1869,  although  it  was  still  impossible 
for  him  to  drag  himself  about  his  room,  he  was  so 
much  excited  by  the  contradictions  that  his  system  of 
culture  had  aroused  that  he  wished  to  start  again  for 
Alais.  '  Aided  by  the  method  of  artificial  cultivation,' 
he  remarked,  '  we  shall  soon  annihilate  these  latest 
oppositions.  There  is  here  both  a  scientific  principle 
and  an  element  of  national  wealth.' 

His  wish  could  not  be  opposed,  but  a  terrible  and 
anxious  journey  it  was  !  At  some  leagues  from  Alais, 
at  a  place  called  Saint  Hippolyte-du-Fort,  where  the 
earliest  experiments  were  made,  Pasteur  stopped.  He 
installed  himself — we  might  rather  say  he  encamped 
— with  his  family  and  his  assistants,  in  a  more  than 
humble  lodging,  one  of  those  miserable,  cold,  paved 
houses  of  the  rural  districts.  Seated  in  his  arm- 
chair, Pasteur  directed  the  experiments,  and  verified 
the  observations  which  he  had  made  the  year  before. 
Each  of  his  predictions  as  to  the  destiny  of  the  dif- 
ferent groups  of  worms  was  fulfilled  to  the  smallest 
detail.  In  the  following  spring  he  left  for  Alais, 
where  he  followed  in  all  their  phases,  from  the  egg 
up  to  the  cocoon,  the  cultivations  there  undertaken, 
and  he  had  the  happiness  of  proving  once  more  the 
certainty  of  his  method. 


166  LOUIS  PASTEUE. 

But  opposition  still  continued.  The  French 
Government,  shaken  by  the  violence  and  tenacity  of 
the  opponents,  hesitated  to  decide  upon  this  process 
of  culture.  The  Emperor  interposed  ;  he  instructed 
Marshal  Vaillant  to  propose  to  Pasteur  to  go  into 
Austria  to  the  Villa  Vicentina,  which  belonged  to  the 
Prince  Imperial.  For  ten  years  the  silk  harvest  at 
this  place  had  not  sufficed  to  pay  the  cost  of  eggs. 
Pasteur  accepted  with  joy  the  prospect  of  a  great 
decisive  experiment.  He  traversed  France  and  Italy, 
reclining  in  a  railway  carriage  or  in  an  arm-chair, 
and  at  last  arrived  at  the  Imperial  villa  near  Trieste. 
Pasteur  succeeded  in  a  marvellous  manner.  The 
sale  of  the  cocoons  gave  to  the  villa  a  nett  profit  of 
twenty-six  million  francs.  The  Emperor,  impressed 
with  the  practical  value  of  the  system,  nominated 
Pasteur  a  Senator,  in  the  month  of  July  1870.  But 
this  nomination,  like  so  many  other  things,  was  swept 
away  before  it  had  time  to  appear  in  the  '  Journal 
Officiel.'  Pasteur,  however,  cared  little  for  the  title 
of  Senator.  He  returned  to  France  on  the  eve  of  the 
declaration  of  war. 

A  patriot  to  the  heart's  core,  he  learned  with 
poignant  grief  the  news  of  his  country's  disasters.  The 
bulletins  of  defeat,  which  succeeded  each  other  with 
mournful  monotony,  threw  him  into  deep  despair.  For 
the  first  time  in  his  life  he  had  not  the  strength  to 
work.  He  lived  at  his  little  house  hi  Arbois  as  one 


DECISIVE  EXPERIMENTS.  167 

completely  vanquished.  Those  who  went  into  his 
room  found  him  often  bathed  in  tears.  On  January 
18,  1871,  he  wrote,  to  the  Dean  of  the  Academy 
of  Medicine  at  the  University  of  Bonn,  a  letter 
in  which  all  his  grief  and  all  his  pride  as  a 
Frenchman  were  displayed,  requesting  him  to  with- 
draw the  diploma  of  German  doctor  which  the 
Faculty  of  Medicine  of  the  University  had  conferred 
upon  him  in  1868.  "Whilst  he  wrote  this  letter, 
which  was  a  cry  of  patriotism,  his  son,  enrolled  as  a 
volunteer,  though  hardly  eighteen  years  of  age,  was 
gallantly  doing  his  duty  in  the  Army  of  the  East. 


168  LOUIS  PASTEUR. 


STUDIES   ON  BEER. 

THE  war  was  over.  Little  by  little  the  life  of  the 
country  was  resumed,  and  with  returning  hope  the 
desire  and  necessity  for  renewed  work.  After  two 
years  of  infirmity,  Pasteur  at  length  began  to  feel 
the  recovery  of  health.  It  was  like  a  slow  and  gentle 
renewal  of  all  things.  He  wished  to  return  as  soon 
as  possible  to  his  laboratory  in  Paris  to  put  into  exe- 
cution projects  of  experiments  which  had  long  been 
working  in  his  brain.  At  the  moment  when  he  was 
preparing  to  start,  the  rebellion  of  the  Commune  broke 
out.  M.  Duclaux,  who  had  become  Professor  of  the 
Faculty  of  Sciences  in  Clermont-Ferrand,  offered  the 
use  of  his  laboratory  to  his  old  master.  Pasteur  ac- 
cepted it.  Eager  to  commence  an  investigation  which 
would  bring  him  again  to  the  study  of  fermentation, 
he  attacked  the  diseases  of  beer.  But  it  was  not  only 
for  the  purpose  of  creating  a  new  link  between  these 
researches  and  his  former  ones  that  he  occupied  him- 
self with  this  subject,  he  was  also  influenced  by  a 
somewhat  patriotic  idea.  He  dreamt  of  success  in  an 


STUDIES  ON  BEEK.  169 

industry  in  which  Germany  is  superior  to  France.  He 
hoped  by  means  of  scientific  principles,  by  which  com- 
merce would  largely  profit,  to  succeed  in  making  for 
French  beer  a  reputation  equal,  if  not  superior,  to 
that  of  Germany. 

Beer  is  much  more  liable  to  contract  diseases  than 
wine.  It  may  be  said  that  while  old  wine  is  often  to  be 
found,  there  is  no  such  thing  as  old  beer.  It  is  con- 
sumed as  fast  as  it  is  made.  Less  acid  and  less 
alcoholic  than  wine,  beer  is  more  laden  with  gummy 
and  saccharine  matters,  which  expose  it  to  rapid 
changes.  Thus  the  trade  in  this  beverage  is  constantly 
struggling  with  the  difficulties  of  its  preservation. 

The  manufacture  of  beer  is  simple.  It  is  extracted 
from  germinated  barley,  or  malt,  an  infusion  of  which 
is  made  and  gradually  heated  to  the  boiling  point. 
It  is  then  flavoured  by  hops.  '  When  the  infusion  of 
malt  and  hops,  which  is  called  '  wort,'  is  completed, 
it  is  subjected  to  a  cooling  process,  and  drawn  off  into 
tuns  and  barrels.  It  is  then  that  alcoholic  fermenta- 
tion sets  in.  The  cooling  ought  to  be  performed 
rapidly.  While  the  wort  is  at  a  high  temperature 
there  is  nothing  to  fear,  it  remains  sound  ;  but  under 
70°  Centigrade,  and  particularly  between  25°  and  35°, 
it  is  easily  attacked  by  injurious  ferments— acetic, 
lactic,  or  butyric.  After  the  wort  is  cooled,  a  little 
of  the  yeast  proceeding  from  a  former  fermentation. 


170  LOUIS  PASTEUE. 

is  added  to  it,  in  order  that  the  whole  mass  of  the 
wort  should  be  invaded  as  soon  as  possible  after  its 
cooling  by  the  alcoholic  ferment  alone — the  only  one, 
properly  speaking,  which  can  produce  beer.  If  this 
wort  were  treated  in  the  same  way  as  the  must  of 
the  grape,  if  it  were  abandoned  to  fermentation  with- 
out yeast — to  so-called  spontaneous  fermentation — 
this  would  hardly  ever  be  purely  alcoholic,  as  in  the 
must  of  grapes,  which  is  protected  by  its  acidity. 
Most  frequently,  instead  of  beer,  an  acid  or  putrid 
liquid  would  be  obtained.  Divers  fermentations 
would  simultaneously  take  place  in  it.  When  the 
wort  has  fermented  and  the  beer  is  made,  there  is 
still  the  fear  of  its  rapid  deterioration,  which  necessi- 
tates its  being  quickly  consumed.  This  condition 
is  sometimes  disastrous  to  those  employed  in  the 
beer  trade ;  and  the  improvements  in  the  manufac- 
ture of  beer  which  have  been  made  during  the  last 
forty  years  have  all  had  for  their  object  the  removal  of 
this  necessity  for  the  daily  production,  so  to  speak,  of 
an  article  of  which  the  consumption  is  liable  to  con- 
stant variations. 

Formerly  only  one  kind  of  beer  was  known,  the 
.beer  of  high  fermentation.  The  wort,  after  having 
undergone  cooling  in  the  troughs,  is  collected  in  a 
large  open  vat  at  a  temperature  of  20°,  and  yeast  is 
added  to  it.  When  the  fermentation  begins  to  show 
itself  on  the  surface  of  the  liquid,  by  the  formation  of 


STUDIES   ON  BEER.  171 

a  light  white  froth,  the  wort  is  transferred  to  a 
series  of  small  barrels,  which  are  placed  in  cellars 
or  store-rooms,  kept  at  a  temperature  of  from  18° 
to  20°  Centigrade.  The  activity  of  the  fermentation 
soon  causes  a  foam  to  rise,  which  becomes  more 
and  more  thick  and  viscous.  This  is  owing  to  the 
abundance  of  yeast  which  it  contains.  This  yeast, 
collected  in  a  large  trough  placed  under  the  casks, 
is  gathered  up  for  future  operations.  The  fermenta- 
tion lasts  for  three  or  four  days,  then  the  beer  is 
made  and  has  become  clear ;  the  bungs  are  fixed 
in  the  barrels,  and  they  are  sent  direct  to  the  retail 
dealer  or  to  the  consumer.  During  the  transit,  a 
certain  quantity  of  yeast,  fallen  to  the  bottom  of  the 
casks,  thickens  the  beer,  but  a  few  days  of  repose  suffice 
to  make  it  again  clear  and  fit  to  drink,  or  to  be  bottled. 

This  system  of  '  high '  fermentation  (so  called  be- 
cause it  begins  at  a  temperature  of  18°  to  20°,  and  is 
raised  one  or  two  degrees  higher  by  the  act  of  fer- 
mentation itself)  is  very  commonly  practised  in  the 
north  of  France,  and  to  a  greater  extent  in  the 
breweries  of  England.  Ale,  pale  ale,  bitter  beer,  are 
all  beers  from  high  fermentation. 

The  '  low  '  fermentation,  which  is  almost  exclusively 
employed  in  Germany,  and  which  is  spreading  more 
and  more  in  France,  consists  in  a  slow  fermentation, 
at  low  temperature,  during  which  the  yeast  settles 
at  the  bottom  of  the  tubs  and  casks.  The  wort, 


172  LOUIS  PASTEUK. 

after  it  has  been  cooled,  is  passed  into  open  wooden 
tuns,  and  the  working  of  the  yeast  takes  place  at  a  tem- 
perature of  about  6°  Centigrade.  This  temperature  is 
maintained  by  means  of  floats,  in  the  form  of  cones 
or  cylinders,  thrown  into  the  fermenting  tuns  and 
kept  filled  with  ice.  The  fermentation  lasts  for  ten. 
fifteen,  and  even  twenty  days.  When  the  beer  is 
drawn  off,  the  yeast  is  collected  from  the  bottom  of  the 
fermenting  tuns.  This  kind  of  beer,  which  is  some- 
times called  German  beer,  sometimes  Strasburg  beer, 
is  generally  much  more  esteemed  than  the  other,  but 
it  requires  certain  expensive,  or  at  least  inconvenient, 
conditions.  There  must  be  ice-caves,  where  the  tem- 
perature is  maintained  all  the  year  round  at  a  few 
degrees  only  above  zero.  This  makes  it  necessary  to 
have  enormous  piles  of  ice.  It  has  been  calculated  that 
for  one  single  hectolitre  of  good  beer,  from  the  begin- 
ning of  the  cooling  of  the  wort  until  the  time  when  it 
is  fit  for  sale,  100  kilogrammes  of  ice  are  required. 
The  '  low  '  beer,  called  also  Mere  de  garde,  beer  for  keep- 
ing, is  principally  manufactured  in  winter,  and  is 
preserved  in  ice-caves  until  the  summer. 

It  is  not  only  the  taste  of  the  consumers  which 
has  favoured  the  manufacture  of  beer  of  low  fermen- 
tation everywhere  except  in  England  ;  it  is  also  the 
advantage  this  beer  possesses  in  being  much  less  liable 
to  deterioration  than  the  other.  By  employing  ice,  the 
brewer  may  manufacture  in  winter,  or  in  the  beginning 


STUDIES   ON   BEEE.  173 

of  spring,  and  thus  place  himself  in  a  position  to  meet 
the  demands  of  consumption  without  fear  of  seeing 
his  beer  attacked  by  disease. 

All  the  diseases  of  beer,  as  Pasteur  has  shown, 
are  caused  exclusively  by  the  development  of  little 
microscopic  fungi,  or  organised  ferments,  the  germs 
of  which  are  brought  by  the  dust  constantly  floating 
in  the  air,  or  which  gets  mixed  with  the  original  sub- 
stances used  in  the  manufacture.  'By  the  expression 
diseases  of  wort  and  of  beer,  I  mean,'  said  Pasteur, 
*  those  serious  alterations  which  affect  the  quality  of 
these  liquids  so  as  to  render  them  disagreeable  to  the 
taste,  especially  when  they  have  been  kept  for  some 
time,  and  which  cause  the  beer  to  be  described  as 
sharp,  sourish,  turned,  ropy,  putrid.'  The  wort  of  beer, 
after  it  has  been  raised  to  the  boiling  heat,  may,  as 
Pasteur's  experiments  testify,  be  preserved  indefinitely, 
even  in  the  highest  atmospheric  temperatures,  when 
in  contact  with  air  free  from  the  germs  of  the  lower 
microscopic  organisms.  The  must,  leavened  by  the 
addition  of  pure  yeast,  kept  free  from  foreign  organ- 
isms, contains  nothing  but  the  alcoholic  ferment,  and 
undergoes  no  other  changes  than  those  due  to  the 
action  of  the  oxygen,  which  does  not  give  rise  to 
acidity,  putridity,  or  bitterness.  Since  the  causes  of 
deterioration  are  the  same  in  beer  as  in  wine,  would 
it  not  appear  as  if  the  action  of  heat  must  be  the  best 


174  LOUIS  PASTEUR. 

preservative  ?  But  beer  is  a  drink  necessarily  charged 
with  carbonic  acid,  and  the  application  of  heat  to  con- 
siderable masses  of  the  liquid  would  expel  this  gas. 
It  would  be  a  very  complicated  business  to  attempt  to 
preserve  this  gas,  or  to  introduce  it  afresh  after  it  had 
been  expelled.  This  difficulty  does  not  arise  when  the 
beer  is  bottled.  At  a  temperature  of  50°  to  55°, 
the  process  of  heating  not  only  cannot  take  away 
from  the  beer  all  its  carbonic  acid,  but  it  does  not 
prevent  the  secondary  fermentation  from  taking  place 
to  a  certain  extent,  and  this  allows  of  the  beer  being 
heated  immediately  after  it  is  put  into  bottles.  This 
heating  of  the  beer  is  practised  on  a  large  scale  in 
Europe  and  in  America.  In  honour  of  Pasteur  the 
process  is  called  Pasteurisation,  and  the  beer  Pas- 
teurised beer. 

But  Pasteur  was  not  content  with  simply  destroying 
the  ferments  of  these  diseases,  he  wished  above  all  to 
prevent  their  introduction.  At  the  moment  when 
the  wort  is  raised  to  the  boiling-point,  when  the 
germs  of  disease  are  destroyed  by  the  heat,  if  the 
cooling  of  the  wort  is  effected  in  contact  with  both 
air  and  yeast  free  from  exterior  germs,  the  beer  may 
be  made  under  conditions  of  exceptional  purity.  Some 
brewers,  taking  for  their  basis  Pasteur's  principles,  con- 
structed an  apparatus  which  enabled  them  to  protect 
the  wort  while  it  was  cooling  from  the  organisms  of 
the  air,  and  to  ferment  this  wort  with  a  leaven  as 


STUDIES  ON  BEER.  175 

pure  as  possible.  At  the  Exhibition  of  Amsterdam 
there  might  be  seen  bottles  half  full,  containing  a  per- 
fectly clear  beer,  which  had  been  tapped  from  the 
time  of  opening  of  the  Exhibition.  This  was  French 
beer,  manufactured  according  to  Pasteur's  principles, 
by  a  great  brewer  of  Marseilles,  M.  Velten.  The 
happy  effect  of  these  studies  is  universally  recognised. 
At  Copenhagen,  M.  Jacobsen  has  had  a  bust  of  Pasteur, 
by  Paul  Dubois,  placed  in  the  salle  d'honneur  of  his 
celebrated  laboratory. 

In  terminating  his  Studies  on  Beer,  Pasteur  re- 
called to  mind  the  principles  which  for  twenty  years 
had  directed  his  labours,  the  resources  and  applica- 
tions of  which  appeared  to  him  unlimited.  '  The 
etiology  of  contagious  diseases,'  he  wrote  with  a  scien- 
tific certainty  of  conviction,  '  is  on  the  eve  of  having 
unexpected  light  shed  upon  it.' 
10 


176  LOUIS  PASIEUE. 


VIRULENT  DISEASES. 

SPLENIC    FEVER    (CHAKBON)  — SEPTICAEMIA. 

*  HE  that  thoroughly  understands  the  nature  of  fer- 
ments and  fermentations,'  said  the  physicist  Eobert 
Boyle,  '  shall  probably  be  much  better  able  than  he 
that  ignores  them,  to  give  a  fair  account  of  divers 
phenomena  of  certain  diseases  (as  well  fevers  as 
others),  which  will  perhaps  be  never  properly  under- 
stood without  an  insight  into  the  doctrine  of  fermen- 
tations.' 

At  all  times,  medical  theories,  more  particularly 
those  which  concern  the  etiology  of  virulent  diseases, 
have  had  to  encounter  the  opposition  of  explanations 
invented  to  account  for  the  phenomena  of  fermenta- 
tion. When  Pasteur  in  1856  began  his  labours  on 
these  subjects,  the  ideas  of  Liebig  were  everywhere 
revived.  Like  the  ferments,  so  the  viruses  and 
processes  of  disease  were  considered  as  the  results  of 
atomic  motions  proper  to  substances  in  course  of 
molecular  change,  and  able  to  communicate  themselves 
to  the  diverse  constituents  of  the  living  body. 

The  researches  of  Pasteur  on  the  part  played  by 


VIEULENT  DISEASES.  177 

microscopic  organisms  in  fermentation,  changed  the 
course  of  these  ideas.  The  ancient  medical  theory  of 
parasites  and  living  contagia  was  revived.  A  German 
Professor,  Dr.  Traube,  in  1864,  put  forward,  in  one  of 
his  clinical  lectures,  a  new  doctrine  of  the  ammoniacal 
fermentation  of  urine. 

'  For  a  long  period,'  he  said,  '  the  mucus  of  the 
bladder  was  regarded  as  the  agent  of  the  alkaline 
decomposition  of  urine.  It  was  supposed  that,  in 
consequence  of  the  distension  produced  by  the  reten- 
tion of  the  liquid,  the  irritated  bladder  produced  a 
larger  quantity  of  mucus,  and  this  mucus  was  re- 
garded as  the  ferment  which  brought  about  the 
decomposition  of  urea,  by  an  innate  chemical 
force.  This  opinion  (which  was  that  of  Liebig)  can- 
not hold  its  ground  in  presence  of  the  researches  of 
Pasteur.  This  investigator  has  demonstrated,  in  the 
most  decisive  manner,  that  alkaline  fermentation,  like 
alcoholic  and  acetic  fermentation,  is  produced  by 
living  organisms,  the  pre-existence  of  which  in  the 
liquid  is  the  sine  qua  non  of  the  process.'  And  Dr. 
Traube,  citing  some  facts  which  confirmed  the  doc- 
trine of  Pasteur,  concluded  thus  :  '  Notwithstanding 
the  long  retention  of  the  urine,  its  alkaline  fermenta- 
tion is  not  produced  by  an  increased  secretion  of 
mucus  or  of  pus ;  it  only  begins  to  develop  from 
the  moment  when  the  germs  of  vibrios  find  access 
to  the  bladder  from  without. 


178  LOUJS  PASTEUK. 

The  opposite  doctrines  of  Liebig  and  Pasteur 
are  here  brought  into  clear  juxtaposition ;  and  thus 
was  their  mutual  and  reciprocal  influence  established 
in  dealing  with  the  etiology  of  one  of  the  most  serious 
diseases  of  the  bladder.  So  far  back  as  1862,  Pasteur, 
in  his  memoir  on  spontaneous  generation,  had  an- 
nounced, contrary  to  all  the  notions  then  held,  that 
whenever  urine  becomes  ammoniacal,  a  little  micro- 
scopic fungus  is  the  cause  of  this  alteration.  Later 
on  he  established  that  in  affections  of  the  bladder 
ammoniacal  urine  was  never  found  without  the  pre- 
sence of  this  fungus ;  and  in  order  to  show  how  in 
these  studies  therapeutic  application  often  runs  hand 
in  hand  with  scientific  discovery,  Pasteur,  having 
proved,  with  his  assistant,  M.  Joubert,  that  boracic 
acid  is  antagonistic  to  the  development  of  the  am- 
moniacal ferment,  advised  Dr.  Guyon,  Clinical  Pro- 
fessor of  Urinary  Diseases  in  the  Faculty  of  Paris,  to 
combat  the  dangerous  ammoniacal  fermentation  by 
injection  of  boracic  acid  into  the  bladder.  The 
celebrated  surgeon  hastened  to  follow  this  advice,  and 
with  the  most  happy  results.  While  attributing  to 
Pasteur  the  honour  of  this  discovery,  M.  Guyon,  in 
one  of  his  lectures,  said : — 

'  Boracic  acid  has  this  immense  advantage,  that  it 
can  be  applied  in  large  doses — 3  to  4  per  cent. — with- 
out causing  the  slightest  pain.  It  has  therefore 
become,  in  our  practice,  the  agent  continually  and 


VIRULENT   DISEASES.  179 

successfully  used  for  injections.  I  also  have  recourse 
to  a  solution  of  boracic  acid  to  produce  large  evacua- 
tions after  the  operation  of  breaking  up  stones  in  the 
bladder  (lithotrity).  I  never  omit  to  use  this  anti- 
septic agent  in  operations  where  breaking  up  is  re- 
quired, and  I  never  wash  the  bladders  of  lithotritised 
patients  with  any  other  substance.  I  have  also  had 
good  results  from  copiously  washing  the  bladders 
and  the  wounds  of  patients  on  whom  lithotomy  has 
been  performed  with  boracic  acid.  I  always  finish 
the  operation  by  prolonged  irrigations  with  a  solution 
of  from  3  to  4  per  cent.' 

It  was  not  only  into  France  and  Germany  that 
Pasteur's  ideas  penetrated ;  in  England,  surgery  bor- 
rowed from  Pasteur's  researches  important  thera- 
peutic applications.  In  1865  Dr.  Lister  began  in 
Edinburgh  the  brilliant  series  of  his  triumphs  in 
surgery  by  the  application  of  his  antiseptic  method, 
now  universally  adopted.  In  the  month  of  February 
1874  in  a  letter  which  does  honour  to  the  sincerity 
and  modesty  of  the  great  English  surgeon,  he  wrote 
to  Pasteur  as  follows  : — 

'  It  gives  me  pleasure  to  think  that  you  will  read 
with  some  interest  what  I  have  written  about  an  or- 
ganism which  you  were  the  first  to  study  in  your 
memoir  on  lactic  fermentation.  I  do  not  know 
whether  you  read  the  '  British  Medical  Journal ;  '  if 
so,  you  will  from  time  to  time  have  seen  accounts  of 


180  LOUJS  PASTEUR. 

the  antiseptic  system  which  for  the  last  nine  years  I 
have  been  trying  to  bring  to  perfection.  Allow  me  to 
take  this  opportunity  of  sending  you  my  most  cordial 
thanks,  for  having,  by  your  brilliant  researches,  de- 
monstrated to  me  the  truth  of  the  germ  theory  of 
putrefaction,  thus  giving  me  the  only  principle  which 
could  lead  to  a  happy  end  the  antiseptic  system. 

Pasteur  followed  with  lively  interest  the  movement 
of  thought  and  the  successful  applications  to  which 
his  labours  had  given  rise.  It  was  a  realisation  of 
the  hopes  he  had  ventured  to  entertain.  Already, 
in  1860,  he  expressed  the  wish  that  he  might  be  able 
to  carry  his  researches  far  enough  to  prepare  the 
way  for  a  profound  study  of  the  origin  of  diseases. 
And,  as  he  gradually  advanced  in  the  discovery 
of  living  ferments,  he  hoped  more  and  more  to 
arrive  at  the  knowledge  of  the  causes  of  contagious 
diseases. 

Nevertheless,  he  hesitated  long  before  definitely 
engaging  himself  in  this  direction.  '  I  am  neither 
doctor  nor  surgeon,'  he  used  to  repeat  with  modest  self- 
distrust.  But  the  moment  came  when,  notwithstand- 
ing all  his  scruples,  he  could  no  longer  be  content 
himself  to  play  the  part  of  a  simple  spectator  of  the 
labours  started  by  his  studies  on  fermentation,  on 
spontaneous  generation,  and  on  the  diseases  of  wines 
and  beer.  The  hopes  to  which  his  methods  gave  rise, 
the  eulogies  of  which  they  were  the  object,  obliged 


VIRULENT  DISEASES.  181 

him  to  go  forward.     In  February  1876  Tyndall  wrote 
to  him  thus  : — 

'  In  taking  up  your  researches  relating  to  infusorial 
organisms,  I  have  had  occasion  to  refresh  my  memory 
of  your  labours ;  they  have  revived  in  me  all  the  ad- 
miration which  I  felt  on  first  reading  them.  It  is  my 
intention  to  follow  up  these  researches  until  I  shall 
have  dissipated  every  doubt  that  has  been  raised  as  to 
the  unassailable  exactitude  of  your  conclusions. 

'  For  the  first  time  in  the  history  of  science  wye  are 
able  to  entertain  the  sure  and  certain  hope  that,  in 
relation  to  epidemic  diseases,  medicine  will  soon  be 
delivered  from  empiricism,  and  placed  upon  a  real 
scientific  basis.  When  this  great  day  shall  come, 
humanity  will  recognise  that  it  is  to  you  the  greatest 
part  of  its  gratitude  is  due.' 

Pasteur  approached  the  study  of  viruses  by  seeking 
to  penetrate  into  all  the  causes  of  the  terrible  malady 
called  splenic  fever  (charbon,  Germ.  Milzbrand).  Each 
year  this  disease  decimates  the  flocks  not  only  in  France 
but  in  Spain,  in  Italy,  in  Eussia,  where  it  is  called  the 
Siberian  plague,  and  in  Egypt,  where  it  is  supposed  to 
date  back  to  the  ten  plagues  of  Moses.  Hungary  and 
Brazil  pay  it  a  formidable  yearly  tribute ;  and  to  come 
back  to  France,  the  losses  have  amounted  in  certain 
years  to  from  fifteen  to  twenty  millions  of  francs. 
For  centuries  the  cause  of  this  pest  has  eluded  all  re- 
search ;  and  further,  as  the  malady  did  not  always 


182  LOUIS  PASTEUR. 

exhibit  the  same  symptoms,  but  varied  according  to 
the  kind  of  animal  that  was  smitten  by  it,  the 
disease  was  supposed  to  vary  with  the  species  that 
was  attacked  by  it.  The  splenic  fever  of  the  horse 
was  distinct  from  that  of  the  cow ;  the  splenic  fever  of 
horse  and  cow  were  again  different  from  that  of  the 
sheep.  In  the  latter,  splenic  fever  was  called  sang-de- 
rate  ;  in  the  cow,  it  was  maladie  du  sang ;  in  the  horse, 
splenic  fever ;  in  man,  malignant  pustule. 

It  was  not  until  1850  that  trustworthy  data  were 
first  collected  regarding  the  nature  of  the  malady,  its 
identity  with  and  difference  from  other  maladies. 
From  1849  to  1852  a  commission  of  the  Medical 
Association  of  Eure-et-Loir  made  a  great  number  of 
inoculations,  applied  other  tests,  and  proved  that  the 
splenic  fever  of  the  sheep  is  communicable  to  other 
sheep,  to  the  horse,  to  the  cow,  and  to  the  rabbit ; 
that  the  splenic  fever  of  the  horse  is  communicable  to 
the  horse  and  to  the  sheep  ;  that  the  splenic  fever  of 
the  cow  is  communicable  to  the  sheep,  to  the  horse, 
and  to  the  rabbit.  As  for  the  malignant  pustule 
in  man,  no  doubt  remained  that  it  must  arise  from 
the  same  cause  as  splenic  fever  in  animals.  What 
class  of  men  is  it  that  the  malignant  pustule  most 
frequently  attacks  ?  Shepherds,  cowherds,  cattle 
breeders,  farm  servants,  dealers  in  hides,  tanners, 
wool  cleaners,  knackers,  butchers — all  who  derive 
their  living  from  domestic  animals.  In  handling  con- 


VIRULENT   DISEASES.  183 

taminated  subjects  the  slightest  excoriation  or  scratch 
of  the  skin  is  sufficient  to  allow  the  virus  to  enter. 
When  others  besides  the  class  that  we  have  named 
become  infected,  it  is  because  they  live  in  the  neigh- 
bourhood of  herds  smitten  with  splenic  fever.  There 
are  also  certain  flies  which  transport  the  virus.  Sup- 
pose one  of  these  flies  to  have  sucked  the  blood  of  an 
animal  which  has  died  of  splenic  fever,  a  person 
stung  by  that-  fly  is  forthwith  inoculated  with  the 
virus. 

At  the  very  time  (1850)  when  these  first  experi- 
ments were  being  made  by  the  Medical  Association  of 
the  Eure-et-Loir,  Dr.  Rayer,  giving  an  account  in  the 
'  Bulletin  de  la  Societe  de  Biologie  de  Paris  '  of  the 
researches  he  had  made,  with  his  colleague,  Dr. 
Davaine,  on  the  contagion  of  splenic  fever,  wrote: — 
'  In  the  blood  are  found  little  thread-like  bodies 
about  twice  the  length  of  a  blood  corpuscle.  These 
little  bodies  exhibit  no  spontaneous  motion.' 

This  is  the  date  of  the  first  observation  on  the 
presence  of  little  parasitic  bodies  in  splenic  fever,  but, 
strange  to  say,  no  attention  was  paid  to  these  minute 
filaments.  Eayer  and  Davaine  also  paid  no  atten- 
tion to  them.  This  indifference  lasted  for  thirteen 
years ;  it  would  have  lasted  longer  still,  if  the  parasitic 
origin  of  communicable  diseases  had  not  been  brought 
before  the  mind  by  each  new  publication  of  Pasteur's. 
From  1857  to  1860  it  will  be  remembered  that  he  had 


184  LOUIS  PASTEUE. 

demonstrated  lactic  fermentation,  like  alcoholic  fer- 
mentation, to  be  the  work  of  a  living  ferment ;  in 
1861  he  had  discovered  that  the  agent  of  butyric 
fermentation  consisted  of  little  moving  thread-like 
bodies,  of  dimensions  similar  to  those  of  the  filaments 
discovered  by  Davaine  and  Eayer  in  the  blood  of 
splenic  fever  patients;  in  1861  he  had  announced 
that  no  ammoniacal  urine  existed  without  the  pre- 
sence of  a  microscopic  organism ;  in  1863  he  had 
established  that  the  bodies  of  animals  in  full  health 
are  sealed  against  the  introduction  of  the  germs  of 
microscopic  organisms;  that  blood  drawn  with  suf- 
ficient precaution  from  the  veins  and  the  arteries, 
and  urine  taken  direct  from  the  bladder,  could  be 
exposed  to  the  contact  of  pure  air  without  putre- 
faction, and  without  the  appearance  of  living  thread- 
like organisms  of  any  kind  whatever,  mobile  or 
immobile.  It  was  all  these  facts  which  in  1863 
brought  back  the  attention  of  Davaine,  as  he  himself 
has  acknowledged,  to  the  observation  which  he  had 
made  in  1850. 

'  M.  Pasteur,'  said  M.  Davaine  in  a  communication 
made  to  the  Academy  of  Sciences,  'published  some 
time  ago  a  remarkable  memoir  on  butyric  fermenta- 
tion, which  consists  of  little  cylindrical  rods,  possess- 
ing all  the  characteristics  of  vibrios  or  of  bacteria. 
The  thread-like  corpuscles  which  in  1850  I  saw  in  the 
blood  of  sheep  attacked  with  sang-de-rate,  having 


VIRULENT  DISEASES.  185 

a  great  analogy  with  these  vibrios,  I  was  led  to 
examine  whether  filiform  corpuscles,  analogous  to  or  of 
the  same  kind  as  those  which  determined  the  butyric 
fermentation,  would  not,  if  introduced  into  the  blood 
of  an  animal,  equally  act  the  part  of  a  ferment. 
Thus  would  be  easily  explained  the  alteration,  and  the 
rapid  infection  of  the  mass  of  the  blood,  in  an  animal 
which  had  received  accidentally  or  experimentally  into 
its  veins  a  certain  number  of  these  bacteria — that  is  to 
§ay,  of  this  ferment.' 

But  two  summers  passed  before  M.  Davaine  was 
able  to  procure  a  sheep  affected  with  the  sang -de-rate. 
It  was  only  in  1863  that  he  first  recognised  the 
constant  presence  of  a  parasite,  in  the  blood  of  sheep 
and  rabbits  which  had  died  from  successive  inocula- 
tions with  blood  taken  after  death  or  in  the  last  hours 
of  life.  He  further  proved  that  the  inoculated  animal, 
in  the  blood  of  which  no  parasites  were  as  yet  visible 
with  the  microscope,  had  every  appearance  of  health, 
and  that  in  these  conditions  the  blood  could  not  com- 
municate splenic  fever. 

'In  the  present  state  of  science,'  Davaine  con- 
cluded, '  no  one  would  think  of  going  beyond  these 
corpuscles  to  seek  for  the  agent  of  the  contagion.  This 
agent  is  visible,  palpable ;  it  is  an  organised  being, 
endowed  with  life,  which  is  developed  and  propagated 
in  the  same  manner  as  other  living  beings.  By  its 
presence,  and  its  rapid  multiplication  in  the  blood,  it 


186  LOUIS  PASTEUR. 

without  doubt  produces  in  the  constitution  of  this  liquid, 
after  the  manner  of  ferments,  modifications  which 
speedily  destroy  the  infected  animal.'  '  For  a  long 
time,'  he  repeated,  '  physicians  and  naturalists  have 
admitted  theoretically  that  contagious  diseases,  serious 
epidemic  fevers,  the  plague,  &c.,  are  caused  by  invisible 
animalculae,  or  by  ferments,  but  I  do  not  know  that 
these  views  have  ever  been  confirmed  by  any  positive 
observations.' 

A  few  months  after  the  publication  of  the  results 
obtained  by  Davaine,  two  professors  of  Val-de-Grace, 
MM.  Jaillard  and  Leplat,  sought  to  refute  the  pre- 
ceding conclusions.  After  having  inoculated  rab- 
bits and  dogs  with  various  putrefying  liquids  filled 
with  vibrios,  they  could  not  cause  the  death  of  these 
animals.  To  bring  about  this  result  it  was  necessary 
to  introduce  into  the  blood  of  these  dogs  and  rabbits 
several  cubic  centimeters  of  very  putrid  liquid.  Again 
in  this  case,  which  only  added  another  example  to  the 
experiments  of  Gaspard  and  Magendie  upon  the  action 
of  putrid  liquids,  they  failed  to  generate  any  virulence 
in  the  blood.  Davaine  had  no  difficulty  in  showing 
that  MM.  Jaillard  and  Leplat's  experiments  were  made 
under  conditions  totally  different  from  his  ;  that  he, 
Davaine,  had  not  made  use  of  the  vibrios  or  bacteria 
of  unselected  infusions,  but  of  bacteria  which  had 
been  found  in  the  blood  of  sheep  which  had  died 
from  sang-de-rate.  .;.;: 


VIKULENT  DISEASES.  187 

Jaillard  and  Leplat  returned  to  the  charge,  and 
this  time  with  entirely  new  and  unexpected  experi- 
ments. They  inoculated  some  rabbits,  as  Davaine 
desired,  with  the  blood  of  a  cow  which  had  died  of 
splenic  fever.  The  rabbits  died  rapidly,  but  without 
showing  before  or  after  their  death  the  least  trace  of 
bacteria.  Other  rabbits,  inoculated  with  the  blood  of 
the  first,  perished  in  the  same  manner,  but  it  was 
still  impossible  to  discover  any  parasite  in  their  blood. 
MM.  Jaillard  and  Leplat  offered  Davaine  some  drops  of 
this  blood.  Davaine,  taking  up  the  experiments  of 
his  opponents,  confirmed  the  exactitude  of  the  facts 
they  had  announced,  but  concluded  by  saying  that 
these  two  professors  had  not  employed  true  splenic 
fever  blood,  but  the  blood  of  a  new  disease,  unknown 
up  to  that  time,  which  Davaine  proposed  to  call  the 
cow  disease. 

'  The  blood  which  we  used,'  replied  MM.  Jaillard 
and  Leplat, '  was  furnished  to  us  by  the  director  of  the 
knacker's  establishment  of  Sours,  near  Chartres,  and 
this  director  is  undeniably  competent  as  to  the  know- 
ledge of  splenic  fever.' 

Full  of  sincerity  and  conviction,  MM.  Jaillard 
and  Leplat  recommenced  their  experiments,  using 
this  time  the  blood  of  a  sheep  which  had  died  of  splenic 
fever,  and  which  M.  Boutet,  the  most  experienced 
veterinary  surgeon  of  the  town  of  Chartres,  had  pro- 
cured for  them.  Their  results  were  the  same  as  those 


188  LOUIS  PASTEUR. 

obtained  with  the  blood  of  the  cow.  Notwithstand- 
ing the  replies  of  Davaine,  which,  however,  added 
nothing  to  the  facts  already  adduced  on  one  side  or  the 
other,  it  was  difficult  to  pronounce  decidedly  in  such 
a  debate.  Unprejudiced  minds  received  from  these 
important  discussions  the  impression  that  Jaillard  and 
Leplat,  in  producing  facts  the  exactitude  of  which 
were  admitted  by  Dr.  Davaine  himself,  had  given  a 
blow  to  the  assertions  of  the  latter,  and  that  the 
subject  required,  in  every  case,  new  experimental 
studies. 

In  1876,  a  German  physician,  Dr.  Koch,  took 
up  the  question.  He  confirmed  the  opinion  of 
Davaine,  but  without  in  the  least  producing  convic- 
tion, since  he  threw  no  light  upon  the  facts  adduced 
by  MM.  Jaillard  and  Leplat,  of  which,  indeed, 
he  did  not  even  deign  to  speak.  At  the  very  same 
moment  when  the  memoir  of  Koch  appeared  in 
Germany,  the  eminent  physician  Paul  Bert  came 
forward  to  corroborate  the  opinion  of  Jaillard  and 
Leplat. 

'  I  can,'  said  M.  Paul  Bert,  '  destroy  the  bacteria  in 
a  drop  of  blood  by  compressed  oxygen,  inoculate  with 
what  remains,  and  reproduce  the  disease  and  death 
without  any  appearance  of  bacteria.  Therefore,  the 
bacteria  are  neither  the  cause  nor  the  necessary  effect 
of  the  disease  of  splenic  fever.  It  is  due  to  a  virus.' 

This  was  indeed  the  opinion  of  Jaillard  and  Leplat. 


VIRULENT  DISEASES.  189 

Pasteur,  in  obedience  to  the  necessity  he  felt  to  get  at 
the  fundamental  truth  of  things,  and  also  in  his  eager 
desire  to  discover  some  decisive  proofs  as  to  the 
etiology  of  this  terrible  disease,  resolved  in  his  turn 
to  attack  the  subject. 

Dr.  Koch  had  stated  in  his  memoir  that  the  little 
filiform  bodies,  seen  for  the  first  time  by  Davaine  in 
1850,  had  two  modes  of  reproduction — one  by  fission, 
which  Davaine  had  observed,  and  another  by  bright 
corpuscles  or  spores.  The  existence  of  this  latter 
mode  of  reproduction  Pasteur  had  already  discovered 
in  1865,  reasserted  and  illustrated  in  1870,  as  being 
common  to  the  filaments  of  the  butyric  ferment,  and 
to  all  the  ferments  of  putrefaction.  Was  Dr.  Koch 
ignorant  of  this  important  fact,  or  did  he  prefer  by 
keeping  silence  to  reserve  to  himself  the  advantage  of 
apparent  priority  ? 

In  order  to  solve  the  first  difficulty  which  pre- 
sented itself  to  his  mind — that  is  to  say,  the  question 
as  to  whether  splenic  fever  was  to  be  attributed  to  a 
substance,  solid  or  liquid,  associated  or  not  associated 
with  the  filaments  discovered  by  Davaine,  or  whether  it 
depended  exclusively  upon  the  presence  and  the  life  of 
these  filaments— Pasteur  had  recourse  to  the  methods 
which  for  twenty  years  had  served  him  as  guides 
in  his  studies  on  the  organisms  of  fermentation. 
These  methods,  delicate  as  they  are,  are  very  simple. 
When  he  wished,  for  example,  to  demonstrate  that  the 


190  LOUIS  PASTEUR. 

microbe-ferment  of  the  butyric  fermentation  was  the 
very  agent  of  decomposition,  he  prepared  an  artificial 
liquid  formed  of  phosphates  of  potash,  of  magnesia, 
and  of  sulphate  of  ammonia,  added  to  the  solution  of 
the  fermentable  matter,  and  in  this  medium  he  caused 
the  microbe-ferments  to  be  sown  in  a  pure  state. 
The  microbe  multiplied,  and  provoked  fermentation. 
From  this  liquid  he  could  pass  to  a  second  or  third 
fermentable  liquid  composed  in  the  same  manner, 
and  so  on  in  succession.  The  butyric  fermentation 
appeared  successively  in  each.  Since  the  year  1857 
this  method  was  supreme.  In  this  particular  research 
on  the  disease  of  splenic  fever  Pasteur  proposed 
to  isolate  the  microbe  of  the  infected  blood,  to  cul- 
tivate it  in  a  state  of  purity  in  artificial  liquids,  and 
then  to  come  back  to  the  examination  of  its  action 
on  animals.  But  as,  since  his  attack  of  paralysis 
in  1868,  Pasteur  had  not  recovered  the  use  of  his 
left  hand,  and  consequently  found  it  impossible  to 
carry  on  a  long  series  of  experiments  alone,  he  was 
obliged  to  seek  for  a  courageous  and  devoted  assistant. 
He  found  one  in  a  former  pupil  of  his  at  the  Ecole 
Normale,  M.  Joubert,  now  Professor  of  Physics  at  the 
College  Eollin.  If  M.  Joubert  incurred  the  danger  of 
these  experiments  on  splenic  fever,  he  also  shared 
with  Pasteur,  in  the  Comptes-rendus  of  the  Academy  of 
Sciences,  the  honour  of  the  researches  and  the  triumph 
of  the  discoveries.  >•-••' 


VIRULENT  DISEASES.  191 

On  April  30,  1877,  Pasteur  read  to  the  Academy 
of  Sciences,  in  his  own  name  and  in  that  of  his 
fellow-worker,  a  note  in  which  he  demonstrated,  this 
time  in  a  completely  unanswerable  manner,  that  the 
bacilli  called  bacteria,  bacterides,  filaments,  rods, 
in  a  word  the  bacilli  discovered  by  Davaine  and 
Eayer  in  1850,  constituted  the  only  agent  of  the 
malady. 

A  little  drop  of  splenic  fever  blood,  sown  in 
urine  or  in  the  water  of  yeast,  previously  sterilised — 
that  is  to  say,  rendered  wwputrescible  by  contact  with 
air  free  from  all  suspended  germs — produces  in  a  few 
hours  myriads  of  bacilli  or  of  bacteria.  A  little  drop 
of  this  first  cultivation  sown  in  a  second  flask  contain- 
ing the  same  liquid  as  the  first  and  prepared  with  the 
same  precautions  as  to  sterility  and  purity,  shows  it- 
self no  less  fertile.  Finally,  after  ten  or  twenty 
similar  cultures  the  parasite  is  evidently  freed  from  the 
substances  which  the  initial  drop  of  blood  might  carry 
with  it ;  yet,  if  a  very  small  quantity  of  the  last  cul- 
ture is  injected  under  the  skin  of  a  rabbit  or  a  sheep, 
it  kills  them  in  two  or  three  days  at  most,  with  all  the 
clinical  symptoms  of  natural  splenic  fever. 

It  might  be  objected  that  the  parasite  was  associ- 
ated in  the  cultivating  liquid  with  some  dissolved  sub- 
stance that  it  had  produced  during  its  life  and  which 
acted  as  a  poison.  Pasteur  accordingly  transported 
some  cultivating  tubes  into  the  cellars  of  the  Observa- 


192  LOUIS  PASTEUR. 

tory,  where  a  temperature  absolutely  constant  reigned, 
a  circumstance  which  permits  of  the  deposit  of  all 
the  parasitic  filaments  at  the  bottom  of  the  tubes. 
Inoculating  afterwards  both  with  the  clear  upper 
liquid  and  with  the  deposit  at  the  bottom,  he  found 
that  the  latter  alone  produced  disease  and  death.  It 
is,  then,  the  bacteria  which  cause  splenic  fever.  The 
proof  was  given  and  no  further  doubt  remained. 

I. 

Yes,  splenic  fever  is  no  doubt  produced  by  bacteria 
just  as  itch  is  produced  by  acaries  and  trichinosis 
by  trichinae.  The  only  difference  is  that  the  para- 
site of  splenic  fever  can  only  be  seen  by  means  of  a 
rather  powerful  microscope.  Here,  then,  is  a  disease 
in  the  highest  degree  virulent,  due  in  its  first  cause  to 
the  infinitely  little.  Pasteur  laid  hold  of  and  isolated 
this  terrible  virus.  It  was  in  a  microscopic  parasite, 
and  in  it  alone,  that  the  virulence  of  splenic  fever  re- 
sided. A  great  scientific  fact  had  been  gained.  A 
virus  might  consist  not  of  amorphous  matter,  but  of 
microscopic  beings.  The  virulence  was  due  to  their 
life. 

Liebig,  and  all  the  chemists  and  doctors  who  had 
accepted  and  maintained  his  doctrine,  totally  repudi- 
ated all  vital  action  in  fermentation  as  well  as  in  con- 
tagious and  infectious  diseases.  Dominated  by  their 


VIRULENT  DISEASES.  193 

hypotheses,  they  allowed  themselves  to  be  deceived  by 
false  assimilations  to  facts  of  a  purely  chemical  kind, 
which  appeared  to  them  to  be  connected  with  the  phe- 
nomena of  fermentation  and  virulence. 

Liebig  wrote,  '  By  the  contact  of  the  virus  of  small- 
pox the  blood  undergoes  an  alteration,  in  consequence 
of  which  its  elements  reproduce  the  virus,  and  this 
metamorphosis  is  not  arrested  until  after  the  complete 
transformation  of  all  the  globules  capable  of  decompo- 
sition.' 

This  vague  theory  of  viruses  was  forced  to  give 
way  before  the  multiplied  experiments  of  Pasteur. 
But  before  occupying  himself  with  further  discoveries, 
although  it  had  been  irrefutably  proved  that  the 
microscopic  parasite  was  the  true  contagium,  it  was 
necessary  to  throw  light  upon  the  facts,  mainly  accu- 
rate, which  had  been  announced  by  Jaillard  and 
Leplat,  and  to  bring  them  into  harmony  with  the  facts, 
not  less  certain,  which  had  been  advanced  by  Davaine. 
The  rabbits  which  Jaillard  and  Leplat  had  inoculated 
with  a  drop  of  the  blood  of  a  cow  or  sheep  stricken 
with  splenic  fever,  died  rapidly,  and  the  blood  of  these 
rabbits  was  shown  to  be  also  virulent.  It  was  suffi- 
cient to  inoculate  other  rabbits  with  a  very  minute 
quantity  to  cause  their  death.  But  Jaillard  and 
Leplat  affirmed  that  the  examination  of  that  blood  did 
not  reveal  the  existence  of  any  microscopic  organisms. 
Paul  Bert,  on  his  part,  had  succeeded  in  destroying 


194  LOUIS  PASTEUR. 

the  bacteria  by  compressed  oxygen,  and  yet  the  viru- 
lence had  continued. 

Were  there,  then,  two  kinds  of  virus?  What 
escape  was  there  from  this  darkness  ?  A  new  light 
suddenly  began  to  dawn.  Pasteur  had  already  some 
years  previously  demonstrated  that  the  animal  body 
is  sealed  against  the  introduction  of  lower  organisms 
— that  in  the  blood,  the  urine,  the  muscles,  the  liver, 
the  spleen,  the  kidneys,  the  brain,  the  marrow,  and 
the  nerves,  in  a  normal  state,  no  germ  is  found,  or 
particle  of  any  kind,  known  or  unknown,  which  could 
be  transformed  into  bacteria,  vibrios,  monads,  or  mi- 
crobes. The  intestinal  canal  alone  is  filled  with 
matters  associated  with  a  host  of  germs  and  living 
products  in  process  of  development,  and  in  divers  states 
of  physiological  action.  Not  only  is  its  temperature 
favourable  to  the  life  of  infusoria,  but  it  receives  in- 
cessantly matters  charged  with  the  germs  of  these  mi- 
croscopic organisms.  To  the  upper  portions  of  the 
canal  the  air  still  has  access,  so  that  even  in  the 
stomach  aerobic  microbes  may  be  found,  but  in  the 
lower  parts  of  the  intestinal  canal  oxygen  is  absent, 
and  only  anaerobic  microbes  can  be  developed  there. 
Although  the  life  exerted  in  the  mucous  surface  of  the 
intestines  opposes  itself  to  the  passage  of  those  little 
organisms  into  the  interior  of  the  body,  this  ceases 
to  be  the  case  after  death.  There  is  no  longer  any 
obstacle  to  arrest  or  prevent  them  from  acting  accord- 


VIKULENT  DISEASES.  195 

ing  to  the  respective  laws  of  their  evolution  and  of  the 
decomposing  influence  which  belongs  to  them.  It  is 
by  anaerobic  organisms,  in  fact,  that  the  putrefaction 
of  dead  bodies  is  begun.  They  penetrate  into  the 
organs  and  into  the  blood  as  soon  as  this  liquid  is  de- 
prived of  oxygen ;  and  it  is  not  long  before  this 
happens,  the  oxygen  fixed  in  the  globules  being  soon 
consumed.  In  the  body  of  an  animal  which  has 
died  of  splenic  fever,  putrefaction  is  still  more  rapid, 
because,  through  the  action  of  the  disease,  the  blood  is 
already  in  a  great  degree  deprived  of  oxygen  at  the 
time  of  death.  Nothing  is  more  striking  than  the  rapid 
inflation  and  almost  immediate  putrefaction  of  animals 
which  have  succumbed  to  splenic  fever.  Of  all  the 
vibrios  ready  to  pass  from  the  intestinal  canal  into  the 
network  of  mesenteric  veins  which  surround  the  canal 
those  which  seem  to  take  the  foremost  place  are  the 
septic  vibrios.  These  specially  merit  the  name  of 
vibrios  of  putrefaction,  from  the  very  putrid  gases 
which  result  from  their  action  upon  nitrogenous  and 
sulphurous  substances.  The  others  diffuse  themselves 
more  or  less  slowly  in  the  blood,  but  the  septic  vibrio 
,  takes  almost  immediate  possession  of  the  dead  body. 
Already  after  twelve  or  fifteen  hours,  the  blood  of  the 
diseased  animal,  which  at  the  time  of  its  death  and 
during  the  first  following  hours  contained  exclusively 
the  parasite  of  splenic  fever,  harbours  at  one  and 
the  same  time  both  the  bacillus  of  splenic  fever 


196  LOUIS  PASTEUR 

and  the  septic  vibrio.  Then  occur  the  very  curious 
effects  arising  from  the  anaerobic  nature  of  these 
vibrios,  and  their  opposition  to  the  bacillus  of  splenic 
fever,  which  is  exclusively  aerobic.  Diffused  in  blood 
deprived  of  oxygen  gas,  the  splenic  bacillus  soon 
perishes.  In  its  place  are  to  be  found  amorphous 
granulations  deprived  of  all  virulence.  The  septic 
anaerobic  vibrio,  on  the  contrary,  finds  itself  after 
death  in  the  most  favourable  conditions  for  its  life  and 
development.  Not  only  does  it  penetrate  into  the 
blood  by  the  deep  mesenteric  veins,  but  also  into  the 
liquids  which  ooze  out  of  the  abdomen  and  muscles. 

From  the  antagonism  existing  between  the  physio- 
logical peculiarities  of  the  splenic  bacilli  and  the  septic 
vibrio,  it  results  that  if,  in  order  to  inoculate  an 
animal  capable  of  contracting  the  fever,  a  drop  of  blood 
be  taken  from  one  that  has  just  died  of  it,  and  if  the 
operation  is  performed  during  the  first  few  hours  after 
death,  it  is  certain  to  communicate  to  that  animal 
splenic  fever,  and  splenic  fever  only.  If,  on  the  other 
hand,  the  operation  is  performed  after  a  greater 
number  of  hours — say,  between  twelve  and  twenty,  ac- 
cording to  the  season  of  the  year — then  the  inocula- 
tion of  the  blood  will  communicate,  at  one  and  the 
same  time,  splenic  fever  and  septicaemia — acute  septi- 
caemia, as  it  may  be  called,  because  of  the  rapid 
inflammatory  disorders  that  the  septic  vibrio  causes 
in  the  inoculated  animal.  The  two  diseases  may  be 


VIRULENT  DISEASES.  197 

developed  simultaneously  in  the  inoculated  animal, 
but  generally  one  precedes  the  other.  The  septic 
contagium  is  the  quickest  in  its  action ;  it  generally 
causes  death  before  the  splenic  fever  has  had  time  to 
develop  itself  and  to  produce  appreciable  effects. 

We  are  now  in  a  position  to  explain  all  the  contra- 
dictory results  obtained  by  MM.  Jaillard  and  Leplat  on 
one  side,  and  by  Davaine  on  the  other.  In  a  country 
which  splenic  fever  had  made  famous,  the  Departement 
d'Eure-et-Loir,  they  had  asked  for  a  little  splenic 
fever  blood.  Now,  what  takes  place  in  a  farm  where 
an  animal  has  died  of  this  disease  ?  The  dead  body 
is  thrown  upon  a  dungheap,  or  into  some  shed  or  stall, 
until  the  knacker's  cart  happens  to  pass.  The  knacker 
takes  his  own  time,  and  the  body  often  remains  there 
twenty-four  or  forty-eight  hours.  The  blood  taken 
from  this  animal  is  more  or  less  invaded  by  putrefac- 
tion, and  vibrios  are  mingled  with  the  bacteria  of  splenic 
fever,  the  development  of  which  is  arrested  the  moment 
the  animal  dies.  In  short,  it  may  be  easily  conceived 
that  an  experimenter  writing  to  Chaxtres  to  procure 
some  splenic  fever  blood  might,  without  his  know- 
ledge, or  the  knowledge  of  his  correspondent,  receive 
blood  at  the  same  time  both  splenic  and  septic.  And 
this  septicaemia  is  sometimes  manifold,  for  a  special 
septicaemia  may  be  said  to  correspond  to  every  sort  of 
vibrio  of  putrefaction. 

Such  were  the  circumstances  which,  without  their 


198  LOUIS  PASTEUK. 

being  aware  of  it,  accompanied  Jaillard  and  Leplat's 
researches  upon  splenic  fever  infection.  This  impres- 
sion will  be  derived  from  reading  the  successive 
notes  laid  by  them  before  the  Academy  of  Sciences. 
The  blood  of  the  cow  which  had  died  of  splenic  fever, 
sent  from  the  knacker's  establishment  of  Sours,  and  the 
blood  of  the  sheep  sent  by  M.  Boutet,  must  both  have 
been  taken  from  the  bodies  of  animals  which  had  been 
dead  a  sufficient  number  of  hours  to  render  their  blood 
both  splenic  and  septic  ;  and  it  was  septicaemia,  so 
prompt  in  its  action,  that  had  killed  the  rabbits  of 
Jaillard  and  Leplat.  As  the  examination  of  the  blood 
of  these  animals  showed  no  signs  of  bacteria,  they 
had  concluded,  with  great  apparent  truth,  that  the 
inoculation  of  splenic  blood  could  cause  death  without 
any  appearance  of  these  organisms,  even  while  the 
blood  used  for  inoculation  was  full  of  them.  The 
presence  of  septic  vibrios  in  the  blood  of  the  inoculated 
rabbits  escaped  their  notice.  When  Davaine  replied 
that  Jaillard  and  Leplat  had  not  worked  with  pure 
splenic  blood  he.  had  hit  upon  the  truth,  but  he  could 
not  give  plausible  reasons  for  it.  The  contest  was 
carried  on  by  experiments  in  which,  on  both  sides,  truth 
and  error  were  closely  blended. 

The  work  of  M.  Paul  Bert,  at  the  close  of  1876, 
was  surrounded  with  circumstances  no  less  complex. 
To  thoroughly  understand  them  we  must  call  to  mind 
Pasteur's  discovery  as  to  the  mode  of  reproducing  the 


VIRULENT  DISEASES.  199 

anaerobic  germs  of  putrefaction.     These  vibrios  repro- 
duce themselves  by  spores.     In  the  vibrio  of  acute 
septicaemia  this  is  the  mode  of  generation.     Short  or 
long  jointed  filaments  show  themselves  studded  with 
brilliant   points,  which   are   precisely   the   spores   of 
which  we  speak.     Experience  proves  that  these  spores 
resist  perfectly  the   poisonous  action  of  compressed 
oxygen.     Inoculating  an  animal  with  blood  which  is  at 
the  same  time  septic  and  splenic,  after  the  blood  has 
been  compressed,  the  septic  germs,  remaining  alive, 
produce  death,  although  neither  bacteria  nor  filaments 
may  be  perceptible  in   its  blood   at   the  moment  of 
death.     It  was  likewise  from  Chartres  that  M.  Paul 
Bert  obtained  his  supply  of  splenic  fever  blood.     The 
blood  he  had  received  was  without  doubt  not  only 
splenic  but  also  septic.     The  filaments  of  bacteria  and 
the  filaments  of  septic  vibrios  had  perished  under  the 
influence  of  the  compressed  oxygen ;  but  the  spores  were 
there,  and  the  great  pressure  of  oxygen  gas  had  not 
affected    them.       The    new    contagium    which    had 
appeared,    and    which    had    killed    the    inoculated 
animals,  was  due  to  these  spores. 

As  regards  the  proof  that  this  virulence  in  the 
blood  of  the  body  of  an  animal  which  has  died  of 
splenic  fever  is  really  the  effect  of  the  septic  vibrio, 
Pasteur,  assisted  by  Joubert  and  a  new  assistant,  M. 
Chamberland,  has  given  that  proof,  as  he  did  in  the 

case  of  the  bacterium  of  splenic  fever,  by  resorting  to 
11 


200  LOUIS  PASTEUR. 

the  method  of  successive  cultivations  in  an  artificial 
medium.     These  cultivations,  however,  of  the  septic 
vibrio  require  very  special  precautions  and  conditions. 
They  should  be  carried  on  in  as  perfect  a  vacuum  as 
it  is  possible  to  obtain,  or  in  contact  with  carbonic 
acid   gas  without   the   presence   of  air.     In   contact 
with  air  the  cultivations  of  septic  vibrios  would  prove 
sterile,  because  the  vibrio  is  exclusively  anaerobic  and 
air  kills  it.     If  a  spore  of  this  organism  could  germi- 
nate in  contact  with  the  air,  the  product  of  the  germina- 
tion would  be  at  once  arrested  and  would  perish  by 
the  action  of  the  oxygen.     It  is  exactly  the  contrary 
with  the  bacilli  of  splenic  fever,  which  prove  sterile  in 
a  vacuum  or  in  presence  of  carbonic  acid  gas.     If  one 
of  the  spores  of  the  splenic  fever  bacillus  (for  it  also 
produces  spores)  could  germinate,  the  product  of  the 
germination,  deprived  of  free  oxygen,  would  at  once 
perish.     And,  to  mention  in  passing  a  very  ingenious 
experiment  of  Pasteur's,  we  thus  obtain  a  means  of 
separating  by  culture   the  bacillus   of  splenic  fever 
from   the   septic   vibrio   when   they  are   temporarily 
associated   together.     If  this  mixture  of  pathogenic 
organisms  is  cultivated  in  contact  with  the  air,  the 
bacilli  of  splenic  fever  alone  will  be  developed.     If  this 
same  mixture  is  cultivated  without  air,  either  in  a 
vacuum   or   in  carbonic  acid  gas,  the  septic  vibrio 
alone  will  be  developed.    This  device  of  culture  is  one  of 
the  best  which  can  be  employed  to  demonstrate  that  the 


V1KULEST  DISEASES.  201 

blood  of  a  body  dead  from  splenic  fever  possesses  imme- 
diately after  death  a  single  contagium,  that  of  splenic 
fever,  and  that  twenty-four  hours  after  death,  on  the 
contrary,  there  are  two  contagia,  that  of  splenic  fever 
and  that  of  septicaemia. 

Some  months  ago  a  very  hot  discussion  arose  be- 
tween Pasteur  and  a  commission  formed  principally  of 
professors  of  the  veterinary  school  in  Turin,  regarding 
the  facts  above  mentioned.  One  experiment,  in  the 
success  of  which  Pasteur  was  extremely  interested, 
had  been  made  at  this  school.  Instead  of  employing 
pure  splenic  fever  blood,  free  from  all  contagium,  the 
Italian  professors,  whether  from  ignorance  of  the  pre- 
ceding facts  or  from  inadvertence,  employed  the  blood 
of  a  diseased  sheep,  which,  from  their  own  showing, 
had  been  dead  more  than  twenty-four  hours.  Pasteur 
immediately  wrote,  pointing  out  that  the  commission 
had  done  wrong  in  using  blood  which  must  have  been 
at  the  same  time  splenic  and  septic.  The  Turin  pro- 
fessors grew  angry,  and  affirmed  that  this  assertion  of 
Pasteur's  was  incorrect ;  that  this  sheep's  blood  had 
been  studied  with  care,  and  that  no  filaments  had  been 
found  in  it  except  those  of  splenic  fever ;  and  it  would, 
moreover,  be  marvellous,  they  added  ironically,  that 
Pasteur  from  the  depths  of  his  laboratory  in  Paris 
should  be  able  to  assert  that  this  blood  was  mixed  with 
septic  poison,  whilst  they,  good  observers,  armed  with 


202  LOUIS  PASTEUR. 

a  microscope,  had  had  this  sheep's  blood  under  their 
eyes.    Pasteur  contented  himself  with  replying  that  his 
assertion  rested  upon  a  principle,  and  that  he  was  per- 
fectly able,  without  having  seen  the  blood  of  the  sheep, 
to  affirm  that  under  the  conditions  in  which  it  had 
been  collected  that  blood  was  septic.     A  public  corre- 
spondence  ensued,    but   no   understanding  could   be 
come  to.     Pasteur  then  offered  to  go  himself  to  Turin, 
in  order  to  demonstrate  upon  as  many  bodies  of  sheep 
dead  of  splenic  fever  as  they  would  like  to  give  him, 
that  the  blood  of  these  dead  bodies— at  the  end  of 
twenty-four  hours  if  in  the  month  of  March,  and  in 
twelve  or  fifteen  hours  if  in  the  month  of  June,  would 
be  found  to  be  both  splenic  and  septic.     Pasteur  also 
proposed,  by   appropriate   cultures,    to   withdraw  at 
pleasure  the  splenic  fever  poison  or  the  septic  poison, 
or  the  two  together,  at  the  choice  of  the  Italians.     The 
•Italians,  however,  shrank  from  Pasteur's  proposal  to  pay 
them  a  visit  in  order  to  convince  them  of  their  error. 
The  clearness  and  certainty  of  Pasteur's  assertions 
are  celebrated,  but  what  gives  such  authority  to  all 
that  he  advances  is,  as  M.  Paul  Bert  once  said,  that 
Pasteur's  boldness  of  assertion   is   only  equalled  by 
his  diffidence  when  he   has  not  experiment  to  back 
him   up.      He   never   fights  except  on  ground  with 
which   he   has  made  himself  familiar,  but  then   he 
fights  with  such  resolution,  and  sometimes  with  such 
impetuosity,  that  one  might  say  to  his  adversary,  who- 


VJEULENT  DISEASES.  203 

ever  he  be,  '  Je  vous  plains  de  tomber  dans  ses  mains 
redoutables.' 

•'  Take  care  !  '  said  a  member  of  the  Academy  of 
Sciences  to  a  member  of  the  Academy  of  Medicine, 
who  a  short  time  after  the  incident  just  related  was 
proposing  scientifically  to  '  strangle  '  Pasteur,  '  take 
care  !  Pasteur  is  never  mistaken.' 

One  day,  in  1879,  a  professor  attached  to  a  faculty 
of  medicine  in  one  of  the  provinces  announced  to  the 
Academy  of  Sciences  that  he  had  found,  in  the  blood 
of  a  woman  who  had  died  in  a  hospital  after  two 
weeks'  illness  from  severe  puerperal  fever,  a  considerable 
number  of  motionless  filaments,  simple  or  jointed, 
transparent,  straight,  or  bent,  which  belonged  to  the 
genus  Leptothrix.  Engaged  in  studies  on  puerperal 
fever,  and  having  never  met  with  a  fact  of  this  kind  in 
his  researches,  Pasteur  wrote  at  once  to  this  professor 
to  ask  him  for  a  specimen  of  the  infected  blood.  The 
blood  arrived  at  the  laboratory,  and  some  days  after 
Pasteur  wrote  to  the  doctor,  '  Your  leptothrix  is  no- 
thing else  than  the  bacterium  of  splenic  fever.' 

This  answer  perplexed  the  doctor  very  much.  He 
wrote  to  Pasteur  that  he  did  not  dispute  the  affirma- 
tion, but  that  he  proposed  to  control  it ;  that  if  he 
found  he  had  been  in  error  he  would  publish  it. 

Pasteur  offered  to  send  him  guinea-pigs  which  had 
been  inoculated  with  splenic  fever.  '  You  will  receive 
them  still  living ;  they  will  die  under  your  eyes.  You 


204  LOUIS  PASTEUR. 

will  make  the  autopsy  and  you  will  yourself  recognise 
your  leptothrix.'  The  doctor  accepted  the  test.  Pasteur 
inoculated  three  guinea-pigs,  had  them  placed  in  a  cage 
and  sent  by  rail  to  the  professor.  They  arrived  the 
following  morning  and  died  twenty-four  hours  after- 
wards under  the  doctor's  own  eyes.  The  first  had 
been  inoculated  with  the  infectious  blood  of  the  dead 
woman,  the  second  with  the  bacterium  of  splenic  fever 
blood  from  Chartres,  the  third  with  the  blood  of  a  cow 
which  had  died  of  splenic  fever  in  the  Jura.  At  the 
autopsy  it  was  impossible  to  discover  the  slightest 
difference  in  the  blood  of  the  three  animals.  Not  only 
the  blood  but  the  internal  organs,  and  especially  the 
spleen,  were  in  exactly  the  same  condition. 

Then,  in  the  most  honourable  manner,  the  doctor 
hastened  to  state,  in  a  communication  to  the  Academy 
of  Sciences,  that  he  regretted  doubly  not  having  known 
about  splenic  fever  the  year  before,  as  he  might  have 
been  able,  on  the  one  hand,  to  diagnose  the  formid- 
able complication  which  had  manifested  itself  in  the 
woman  who  died  on  April  4,  1878,  and,  on  the  other 
hand,  to  have  traced  out  the  mode  of  contamination 
which  now  eluded  him.  He  had,  however,  succeeded  in 
learning  a  few  details  regarding  the  unhappy  woman. 
She  was  a  charwoman,  and  lived  in  a  little  room 
adjoining  the  stables  of  a  horse-dealer.  Through 
these  stables  a  large  number  of  horses  passed  con- 
tinually. 


VIRULENT  DISEASES.  205 

But  to  return  to  our  saptic  vibrios.  If  air  de- 
stroys them,  if  their  culture  is  impossible  in  contact 
with  air,  how  can  septicaemia  exist,  since  air  is  every- 
where present  ?  How  can  blood  exposed  to  the  air 
become  septic  from  particles  of  dust  on  the  sur- 
face of  objects  or  which  the  air  holds  in  suspension? 
Where  can  the  septic  germs  be  formed  ?  The  objec- 
tion seems  a  serious  one,  but  it  disappears  before  a 
very  simple  experiment.  Take  some  serum  from 
the  abdomen  of  a  guinea-pig  which  has  died  of  acute 
septicaemia.  It  will  be  found  full  of  septic  vibrios 
in  process  of  generation  by  fission.  Let  this  liquid 
be  then  exposed  to  the  contact  of  air,  with  the  pre- 
caution of  giving  a  certain  depth  to  the  liquid  —say, 
a  centimeter  of  depth.  In  some  hours,  if  examined 
with  the  microscope,  the  following  curious  spectacle 
will  be  witnessed  :  In  the  upper  layers  the  oxygen  of 
the  air  is  absorbed,  which  is  manifested  by  the  already 
changed  colour  of  the  liquid.  There  the  filamentous 
vibrio  dies,  and  disappears  under  the  form  of  fine 
amorphous  granulations  deprived  of  virulence.  At  the 
bottom  of  this  layer  of  one  centimeter  in  thickness,  on 
the  contrary,  the  vibrios,  protected  from  the  approach 
of  oxygen  by  those  of  their  own  kind  which  have 
perished  above  them,  continue  to  multiply  by  fission 
until  by  degrees  they  pass  into  the  state  of  spores  ;  so 
that  instead  of  moving  threads  of  all  dimensions,  the 
length  of  which  sometimes  even  extends  beyond  the 


206  LOUIS  PASTEUR. 

field  of  the  microscope,  nothing  is  now  seen  but  a  dust 
of  brilliant  isolated  specks,  upon  which  the  oxygen  of 
the  air  has  no  action.  It  is  thus  that  a  dust  of  septic 
germs  can  be  formed  even  in  contact  with  air.  And 
thus  it  becomes  possible  to  understand  how  anaerobic 
organisms  may  be  sown  in  putrescible  liquids  by  the 
dust  suspended  in  the  atmosphere.  Thus  also  may 
be  explained  the  permanence  of  putrid  diseases,  even 
of  those  which  are  caused  by  anaerobic  microbes,  that 
cannot  live  in  the  atmosphere  and  which  escape  de- 
struction by  becoming  spores. 

By  means  of  these  experiments,  as  unexpected  as 
they  were  conclusive,  Pasteur  had  demonstrated  that 
Jaillard  and  Leplat  had  not  really  inoculated  their 
rabbits  with  an  amorphous  virus,  liquid  or  solid,  but 
with  a  virus  constituted  of  a  living  microscopic  organ- 
ism— in  other  words,  with  a  true  ferment.  By  the 
side  of  the  parasite  of  splenic  fever  we  have  thus  a 
fresh  example  of  a  living  animated  virus,  with  germs 
forming  dust.  And  the  extraordinary  thing  is  that 
among  the  microbes  of  special  maladies — which  they 
produce  by  penetrating  and  multiplying  in  the  bodies 
of  animals—  are  to  be  found  aerobies  like  the  bacilli  of 
splenic  fever,  and  anaerobies  like  the  vibrios  of  acute 
septicaemia. 


VIRULENT  DISEASES.  207 


II. 

In  these  two  virulent  maladies,  then,  splenic  fever 
and  septicaemia,  the  researches  of  Pasteur  had  clearly 
established  the  parasitic  theory.  A  grand  and  novel 
opening  was  made  for  future  studies  on  the  origin  of 
diseases.  Yet,  judging  from  the  surprising  differences 
•which  separate  septicaemia  and  splenic  fever,  we  can 
foresee  that  should  the  future,  copying  the  past,  in 
regard  to  this  and  still  more  recent  discoveries,  have 
in  store,  as  it  no  doubt  has,  the  knowledge  of  new 
microbes  of  disease,  the  specific  properties  of  these 
microscopic  organisms  will  demand,  for  each  new  ex- 
ploration, ceaselessly  repeated  efforts,  not  only  to  make 
the  existence  of  these  organisms  evident,  but  also  to 
furnish  decisive  proofs  of  their  morbific  power.  But 
the  question  which  may  be  considered  as  already  solved 
is  the  non- spontaneity  of  these  infectious  microbes. 
By  what  is  called  spontaneous  disease  is  meant  parasitic 
disease.  But  in  the  present  state  of  science  sponta- 
neous disease  has  no  more  existence  than  spontaneous 
generation.  Such  aphorisms,  however,  are  not  allowed 
to  pass  without  occasional  contradictions,  all  the  more 
vehement  from  their  rarity.  At  the  International 
Medical  Congress  held  in  London,  August  1881,  Dr. 
Bastian,  who  practises  in  one  of  the  principal  hospitals 
of  London,  declared  that  though  he  was  unable  to 


208  LOUIS  PASTEUR. 

deny  the  existence  of  parasitic  diseases,  yet,  in  his 
opinion,  the  microbes  were  the  effect  and  not  the  cause 
of  these  diseases. 

'  Is  it  possible,'  cried  Pasteur,  who  was  present  at 
the  meeting,  '  that  at  this  day  such  a  scientific  heresy 
should  be  held  ?  My  answer  to  Dr.  Bastian  will  be 
short.  Take  the  limb  of  an  animal  and  crush  it  in  a 
mortar  ;  let  there  be  diffused  in  this  limb,  around  these 
crushed  bones,  as  much  blood,  or  any  other  normal  or 
abnormal  liquid  as  you  please.  Take  care  only  that 
the  skin  of  the  limb  is  neither  torn  nor  laid  open,  and 
I  defy  you  to  exhibit  on  the  following  day,  or  during 
all  the  time  the  malady  lasts,  the  least  microscopic 
organism  in  the  humours  of  this  limb.' 

After  the  example  of  Liebig  in  1870,  Dr.  Bastian 
did  not  accept  the  challenge. 

But  if  a  disease  like  splenic  fever  is  carried  by  a 
microbe,  this  microbe  is  under  the  influence  of  the 
medium  in  which  it  finds  itself.  It  does  not  develop 
everywhere.  Easily  inoculable  and  fatal  to  the  ox, 
the  sheep,  the  rabbit,  and  the  guinea  pig,  splenic  fever 
is  very  rare  in  the  dog  and  in  the  pig.  These  must 
be  inoculated  several  times  before  they  contract  the 
disease,  and  even  then  it  is  not  always  possible  to 
produce  it.  Again,  there  are  some  creatures  which  are 
never  assailable  by  it.  It  can  never  be  taken  by  fowls. 
In  vain  they  are  inoculated  with  a  considerable  quan- 
tity of  splenic  blood;  it  has  no  effect  upon  them. 


VIRULENT  DISEASES.  209 

This  invulnerability  had  very  much  struck  Pasteur 
and  his  two  assistants,  Joubert  and  Chamberland. 
What  was  it  in  the  body  of  a  fowl  that  enabled 
it  to  thus  resist  inoculations  of  which  the  most  in- 
finitesimal quantity  sufficed  to  kill  an  ox?  They 
proved  by  a  series  of  experiments  that  the  microbe 
of  splenic  fever  does  not  develop  when  subjected  to 
a  temperature  of  44°  Centigrade.  Now,  the  tempe 
rature  of  birds  being  between  41  and  42  degrees, 
may  it  not  be,  said  Pasteur,  that  the  fowls  are 
protected  from  the  disease  because  their  blood  is  too 
warm — not  far  removed  from  the  temperature  at  which 
the  splenic  fever  organism  can  no  longer  be  culti- 
vated ?  Might  not  the  vital  resistance  encountered  in 
the  living  fowl  suffice  to  bridge  over  the  small  gap 
between  41-42,  and  44-45  degrees  ?  For  we  must 
always  allow  for  a  certain  resistance  in  all  living 
creatures  to  disease  and  death.  No  doubt,  life  to 
a  parasite  in  the  body  of  an  animal  would  not  be 
as  easy  as  in  a  cultivating  liquid  contained  in  a  glass 
vessel.  If  the  inoculating  microbe  is  aerobic,  it  can 
only  be  cultivated  in  blood  by  taking  away  the  oxygen 
from  the  globules,  which  retain  it  with  a  certain 
force  for  their  own  life.  Nothing  was  more  legitimate 
than  to  suppose  that  the  globules  of  the  blood  of  the 
fowl  had  such  an  avidity  for  oxygen  that  the  fila- 
ments of  the  splenic  parasite  were  deprived  of  it,  and 
that  their  multiplication  was  thus  rendered  impossible. 


210  LOUIS  PASTEUR. 

This  idea  conducted  Pasteur  and  his  assistants  to  new 
researches.  '  If  the  blood  of  a  fowl  was  cooled,'  they 
asked, '  could  not  the  splenic  fever  parasite  live  in  this 
blood?' 

The  experiment  was  made.  A  hen  was  taken,  and, 
after  inoculating  it  with  splenic  fever  blood,  it  was 
placed  with  its  feet  in  water  at  25  degrees.  The 
temperature  of  the  blood  of  the  hen  went  down  to 
37  or  38  degrees.  At  the  end  of  twenty-four  hours 
the  hen  was  dead,  and  all  its  blood  was  filled  with 
splenic  fever  bacteria. 

But  if  it  was  possible  to  render  a  fowl  assailable 
by  splenic  fever  simply  by  lowering  its  temperature, 
is  it  not  also  possible  to  restore  to  health  a  fowl 
so  inoculated  by  warming  it  up  again  ?  A  hen  was 
inoculated,  subjected,  like  the  first,  to  the  cold-water 
treatment,  and  when  it  became  evident  that  the  fever 
was  at  its  height  it  was  taken  out  of  the  water, 
wrapped  carefully  hi  cotton  wool,  and  placed  in  an 
oven  at  a  temperature  of  35  degrees.  Little  by  little 
its  strength  returned ;  it  shook  itself,  settled  itself 
again,  and  in  a  few  hours  was  fully  restored  to  health. 
The  microbe  had  disappeared.  Hens  killed  after 
having  been  thus  saved,  no  longer  showed  the 
slightest  trace  of  splenic  organisms. 

How  great  is  the  light  which  these  facts  throw 
upon  the  phenomenon  of  life  in  its  relation  to  ex- 
ternal physical  conditions,  and  what  important  in- 


VIRULENT  DISEASES.  211 

ferences  do  they  warrant  as  to  the  influence  of  external 
media  and  conditions  upon  the  life  and  develop- 
ment of  living  contagia  !  There  have  been  great  dis- 
cussions in  Germany  and  France  upon  a  mode  of 
treatment  in  typhoid  fever,  which  consists  in  cooling 
the  body  of  the  patient  by  frequently  repeated  baths. 
The  possible  good  effects  of  this  treatment  may  be 
understood  when  viewed  in  conjunction  wyith  the  fore- 
going experiment  on  fowls.  In  typhoid  fever  the  cold 
arrests  the  fermentation,  which  may  be  regarded  as  at 
once  the  expression  and  the  cause  of  the  disease,  just 
as,  by  an  inverse  process,  the  heat  of  the  body  arrests 
the  development  of  the  splenic  fever  microbe  in  the 
hen. 


212  LOUIS  PASTEUR. 


FOWL   CHOLERA. 

IF  fowls  are  naturally  impervious  to  the  infection  of 
splenic  fever,  there  is  a  disastrous  malady  to  which 
they  are  subject,  and  which  is  commonly  called  '  fowl 
cholera.'  Pasteur  thus  describes  the  disorder : — '  The 
bird  which  is  attacked  by  this  disease  is  without 
strength,  staggering,  the  wings  drooping.  The  ruffled 
feathers  of  the  body  give  it  the  shape  of  a  ball.  An 
overpowering  somnolence  takes  possession  of  it.  If 
forced  to  open  its  eyes,  it  appears  as  if  it  were 
awakened  out  of  a  deep  sleep.  Very  soon  the  eyelids 
close  again,  and  generally  death  conies  without  the 
animal  changing  its  place,  or  without  any  struggle, 
except  at  times  a  slight  movement  of  the  wings  for  a 
few  seconds.'  The  examination  after  death  reveals 
considerable  internal  disorders. 

Here,  again,  the  disease  is  produced  by  a  micro- 
scopic organism.  A  veterinary  surgeon  of  Alsace, 
M.  Moritz  by  name,  was  the  first  who  suspected  the 
presence  of  microbes  in  this  disease ;  a  veterinary 
surgeon  of  Turin,  M.  Peroncito,  depicted  it  in  1878 ; 


FOWL  CHOLEEA.  213 

a  professor  of  the  veterinary  school  of  Toulouse,  M. 
Toussaint,  recognised  it,  in  his  turn,  in  1879,  and  sent 
to  Pasteur  the  head  of  a  cock  which  had  died  of 
the  cholera.  But,  however  skilful  they  were,  these 
observers  had  not  succeeded  in  deciding  the  question 
of  parasitism.  None  of  them  had  hit  upon  a  suitable 
cultivating  medium  for  the  parasite,  nor  had  they 
reared  it  in  successive  crops.  This,  however,  is  the 
only  method  of  proving  that  the  virulence  belongs 
exclusively  to  a  parasite. 

It  is  absolutely  necessary,  in  the  study  of  maladies 
caused  by  microscopic  organisms,  to  procure  a  liquid 
where  the  infectious  parasite  can  grow  and  multiply 
without  possible  mixture  of  other  organisms  of  differ- 
ent kinds.  An  infusion  of  the  muscles  of  the  fowl, 
neutralised  by  potash,  and  rendered  sterile  by  a  tem- 
perature of  110  to  115  degrees,  has  proved  to  be 
wonderfully  appropriate  to  the  culture  of  the  microbe 
of  fowl  cholera.  The  facility  of  its  multiplication  in 
this  medium  is  almost  miraculous.  In  some  hours 
the  clearest  infusion  begins  to  grow  turbid,  and  is 
found  to  be  filled  with  a  multitude  of  little  organisms 
of  an  extreme  tenuity  slightly  strangulated  at  their 
centres.  These  organisms  have  no  movement  of  their 
own.  In  some  days  they  change  into  a  multitude 
of  isolated  specks,  so  diminished  in  volume  that  the 
liquid,  which  had  been  turbid  to  the  extent  of  resembling 
milk,  becomes  again  almost  as  clear  as  at  first.  The 


214  LOUIS  PASTEUR. 

microbe  here  described  belongs  to  a  totally  different 
group  from  that  of  the  vibrios.  It  is  ranged  under  the 
genus  called  ' micrococci.'  'It  is  in  this  group,'  said 
Pasteur  on  one  occasion,  'that  the  microbes  of  the 
viruses  which  are  yet  unknown  will  probably  be  one 
day  found.' 

In  the  cultivation  of  the  microbe  of  fowl  cholera, 
Pasteur  tried  one  of  the  cultivating  liquids  which  he 
had  previously  made  use  of  with  most  success— the 
water  of  yeast — that  is  to  say,  a  decoction  of  yeast  in 
water  rendered  clear  by  nitration  and  then  sterilised  by 
a  temperature  of  over  100  degrees.  The  most  diverse 
microscopic  organisms  find  in  this  liquid  suitable 
nourishment,  particularly  if  it  has  been  neutralised. 
When,  for  example,  the  bacterium  of  splenic  fever  is 
sown  in  the  liquid,  it  assumes  in  a  few  hours  a  sur- 
prising development.  Now,  it  is  remarkable  that  this 
medium  is  quite  unsuited  to  the  life  of  the  microbe  of 
fowl  cholera.  Not  only  does  it  not  develop,  but  the 
microbe  perishes  in  this  liquid  in  less  than  forty-eight 
hours.  May  we  not  connect  this  singular  fact  with 
that  which  is  observed  when  a  microscopic  organism 
proves  innocuous  in  an  animal  which  has  been  ino- 
culated with  it  ?  It  is  innocuous  because  it  cannot 
develop  itself  in  the  body  of  the  animal,  or  because, 
its  development  being  arrested,  it  cannot  attain  the 
vital  organs. 

The  decoction  extracted  from  the  muscles  of  the 


FOWL  CHOLERA.  215 

fowl  is  the  only  medium  which  really  suits  the  mi- 
crobe of  fowl  cholera.  It  suffices  to  inoculate  the  fowl 
with  the  hundredth,  even  the  thousandth,  part  of  a 
drop  of  this  mixture,  to  produce  the  disease  and  cause 
death.  But  here  is  a  strange  peculiarity.  If  guinea- 
pigs  are  inoculated  with  this  little  parasite  they  are 
hardly  ever  killed  by  it.  Guinea-pigs  of  a  certain  age 
generally  exhibit  only  a  local  lesion  at  the  point  of 
inoculation,  which  ends  in  an  abscess  more  or  less 
prominent.  After  opening  spontaneously,  the  abscess 
closes  again  and  heals,  while  the  animal  preserves  its 
appetite  and  its  appearance  of  health.  These  abscesses 
sometimes  last  several  weeks.  They  are  surrounded 
by  a  pyogenic  membrane  and  filled  with  a  creamy 
pus,  in  which  the  microbe  swarms  side  by  side  with  the 
pus  globules.  It  is  the  life  of  the  microbe  inoculated 
under  the  skin  which  causes  the  abscess.  The  abscess, 
with  the  membrane  which  surrounds  it,  becomes  for 
the  little  organism  a  sort  of  closed  vessel,  which  it  is 
even  easy  to  tap  without  sacrificing  the  guinea-pig. 
The  organism  is  mixed  with  the  pus  in  a  state  of  great 
purity,  and  although  it  is  localised  its  virulence  is  ex- 
treme. When  fowls  are  inoculated  with  the  contents 
of  the  abscess  they  die  rapidly,  while  the  guinea-pig, 
which  has  furnished  the  virus,  gets  well  without  the 
least  suffering.  A  curious  instance  this  is  of  the 
local  evolution  of  a  very  virulent  microscopic  organism, 
which  produces  neither  internal  disorders  nor  the 


216  LOUIS  PASTEUR. 

death  of  the  animal  upon  which  it  lives  and  multiplies, 
but  which  can  carry  death  to  other  species  inoculated 
with  it.  Fowls  and  rabbits  living  among  the  guinea- 
pigs  suffering  from  these  abscesses  might  in  a  moment 
be  smitten  and  perish,  while  the  health  of  the  guinea- 
pigs  remained  unchanged.  To  produce  this  result  it 
would  suffice  that  a  little  of  the  discharge  from  the 
abscess  of  a  guinea-pig  should  get  smeared  over  the 
food  of  the  fowls  and  rabbits.  An  observer  witnessing 
such  deaths  without  apparent  cause,  and  ignorant  of 
this  strange  dependency,  would  no  doubt  be  tempted 
to  believe  in  the  spontaneity  of  the  disease.  He  would 
be  far  from  supposing  that  the  evil  had  originated  in 
the  guinea-pigs,  which  were  all  in  good  health.  In 
the  history  of  contagia  what  mysteries  may  some  day 
be  cleared  up  by  even  more  simple  solutions  than  this 
one  ! 

When  some  drops  of  the  liquid  containing  this 
microbe  are  placed  on  the  food  of  fowls,  the  disease 
penetrates  by  the  intestinal  canal.  There  the  little 
organism  increases  in  such  great  abundance  that  ino- 
culation with  the  excrements  of  the  injected  fowls  pro- 
duces death.  It  is  thus  easy  to  account  for  the  mode 
of  propagation  of  this  very  serious  disease,  which 
depopulates  sometimes  all  the  poultry  yards  in  the 
country.  The  only  means  of  arresting  the  contagion 
is  to  isolate,  for  a  few  days  only,  the  fowls  and  the 
chickens,  to  remove  the  dung  heaps,  to  wash  the  yard 


FOWL  CHOLEKA.  217 

thoroughly,  especially  with  water  acidulated  with  a 
little  sulphuric  acid,  or  carbolised  water  with  two 
grammes  of  acid  to  the  litre.  These  liquids  readily  de- 
stroy the  microbe,  or  at  least  suspend  its  development. 
Thus  all  causes  of  contagion  disappear,  because,  during 
their  isolation,  the  animals  already  smitten  die.  The 
action  of  the  disease,  in  fact,  is  very  rapid. 

The  repeated  cultivation  of  the  infectious  microbe  in 
the  fowl  infusion,  passing  always  from  one  infusion  to 
the  next  following,  by  sowing  in  the  latter  an  infinitely 
small  quantity,  so  to  speak,  of  the  virus — as  much,  for 
example,  as  may  be  retained  on  the  point  of  a  needle 
simply  plunged  into  the  cultivation— does  not  sensibly 
lessen  the  virulence  of  the  microscopic  organism.  Its 
multiplication  inside  the  bodies  of  fowls  is  quite  as 
easy  with  the  last  as  with  the  first  culture.  In  short, 
whatever  may  be  the  number  of  the  successive  cultures 
of  the  microbe  in  the  fowl  infusion,  the  last  culture  is 
still  very  virulent.  This  proves  the  microbe  to  be  the 
cause  of  the  disease — a  proof  the  same  in  kind  as  that 
which  had  already  enabled  Pasteur  to  show  that 
splenic  fever  and  septicaemia  are  produced  by  specific 
microbes. 

Like  the  bacillus  of  splenic  fever,  the  microbe  of 
the  fowl  cholera  is  an  aerobic  organism.  It  is  culti- 
vated in  contact  with  the  air,  or  in  aerated  liquids. 
At  the  same  time,  though  it  is  entitled  to  be  called  an 
aerobic  organism,  it  differs  essentially  in  certain  re- 


218  LOUIS  PASTEUE. 

spects  from  the  parasite  of  splenic  fever.  If  splenic 
fever  blood  filled  with  filaments  of  the  parasite  be 
enclosed  in  a  vessel  protected  from  the  air — say,  in  a 
tube  closed  at  its  two  extremities — in  a  few  days,  eight 
or  ten  at  the  most,  and  much  fewer  in  summer,  the 
parasite  disappears,  or  rather  is  reduced  to  fine  amor- 
phous granulations,  and  the  blood  loses  all  its  viru- 
lence. If  the  same  system  of  shutting  out  the  air  be 
employed  with  the  blood  of  a  fowl  charged  with  the 
microbe  of  fowl  cholera,  this  microbe  will  be  preserved 
with  its  virulence  for  weeks,  months,  even  years. 
Pasteur  has  been  able  to  keep  for  three  years  tubes 
thus  sealed,  a  drop  of  blood  from  which  when  culti- 
vated in  fowl  infusion,  sufficed  to  infect  the  birds  in 
the  poultry  yard  with  cholera.  And  not  only  is  the 
microbe  preserved  thus  in  the  blood  contained  in  the 
tube ;  the  same  occurs  if  fowl  infusion  be  put  into 
tubes  and  then  sealed  by  the  flame  of  a  lamp. 

When,  in  course  of  time,  such  tubes  lose  their 
virulence,  it  is  because  the  vitality  of  the  organism  is 
extinct.  The  moment  the  contents  of  the  tube  cease 
to  be  virulent,  it  is  a  sign  that  the  contagium  is  dead. 
It  is  useless,  then,  to  attempt  to  cultivate  it :  the 
microbe  cannot  be  revived. 

Here,  then,  is  a  third  virulent  disease,  also  produced 
by  a  microscopic  organism.  The  characteristics  of  fowl 
cholera  are  very  different  from  those  of  splenic  fever 
and  acute  septicemia,  and  these  three  microbes  do  not 


FOWL  CHOLERA.  219 

in  the  least  resemble  each  other.  But,  glancing  back 
over  Pasteur's  work,  are  not  the  diseases  of  silkworms, 
pebrine  and  flacherie,  also  virulent  diseases  ?  Thus, 
in  so  many  things,  through  so  many  studies,  the  same 
connection  holds  good.  Each  discovery  of  Pasteur's  is 
linked  to  those  which  precede  it,  and  is  the  rigorous 
verification  by  experimental  method  of  a  preconceived 
idea. 

'  Nothing  can  be  done,'  said  he  one  day,  '  without 
preconceived  ideas;  only  there  must  be  the  wisdom 
not  to  accept  their  deductions  beyond  what  experi- 
ments confirm.  Preconceived  ideas,  subjected  to  the 
severe  control  of  experimentation,  are  the  vivifying 
flame  of  scientific  observation,  whilst  fixed  ideas  are 
its.  danger.  Do  you  remember  the  fine  saying  of 
Bossuet  ?  "  The  greatest  sign  of  an  ill-regulated 
mind  is  to  believe  things  because  you  wish  them  to  be 
so."  To  choose  a  road,  to  stop  habitually  and  to  ask 
whether  you  have  not  gone  astray,  that  is  the  true 
method.' 

It  -is  this  method  which  conducted  him  in  1880 
to  that  wonderful  discovery,  the  attenuation  of  con- 
tagia.  What  certain  of  these  contagia  are,  we  have 
already  seen.  We  shall  now  learn  what  they  become 
in  the  hands  of  Pasteur. 


220  LOUIS  PASTEUE. 


THE    ATTENUATED   VIRUS,   OR   VACCINA- 
TION OF  VIRULENT  DISEASES. 

THE    VACCINE    OF    FOWL    CHOLEKA. 

AMONG  the  scourges  which  afflict  humanity  there  are 
none  greater  than  virulent  diseases.  Measles,  scar- 
latina, diphtheria,  small-pox,  syphilis,  splenic  fever, 
yellow  fever,  camp  typhus,  the  plague  of  the  East 
— what  a  terrible  enumeration !  I  pass  over  some, 
such  as  glanders,  leprosy,  and  hydrophobia.  The 
history  of  these  diseases  presents  extraordinary  cir- 
cumstances. The  most  strange,  assuredly,  is  that 
which  has  been  from  all  time  established  with  a  great 
number  of  these  diseases,  that  they  are  non-recurrent. 
As  a  general  rule,  notwithstanding  some  rare  excep- 
tions, man  can  only  have  measles,  scarlet  fever, 
plague,  yellow  fever  once.  What  explanation,  even 
hypothetically,  can  be  given  of  such  a  fact?  Still 
more  difficult  is  it  to  explain  how  vaccination,  which  is 
itself  a  virulent  though  benign  disease,  preserves  from 
a  more  serious  malady,  the  small-pox?  Has  there 


THE  ATTENUATED  VIRUS,   OR  VACCINATION.     221 

ever  been  a  discovery  more  mysterious  in  its  causes 
and  origin,  standing,  as  it  does,  alone  in  the  history 
of  medicine,  and  for  more  than  a  century  defying  all 
comparison  ? 

After  dwelling  long  on  Jenner's  discovery  this  ques- 
tion arose  in  Pasteur's  mind :  If  contagious  maladies 
do  not  repeat  themselves,  why  should  there  not  be 
found  for  each  of  them  a  disease  different  from  them, 
but  having  some  likeness  to  them,  which,  acting 
upon  them  as  cow-pox  does  upon  small-pox,  would 
have  the  virtue  of  a  prophylactic  ?  A  chance  occur- 
rence, one  of  those  chances  which  not  unfrequently 
occur  to  those  who  are  steadfastly  looking  out  for 
them,  opened  out  to  Pasteur  the  way  to  a  discovery 
which  may  well  be  called  one  of  the  greatest  discoveries 
of  the  age. 

In  causing  the  microbe  of  fowl  cholera  to  pass  from 
culture  to  culture,  in  an  artificial  medium,  a  sufficient 
number  of  times  to  render  it  impossible  that  the  least 
trace  of  the  virulent  matter  from  which  it  originally 
started  should  still  exist  in  the  last  cultivation, 
Pasteur  gave  in  an  absolute  manner  the  proof  that 
infectious  microbes  are  the  sole  authors  of  the 
diseases  which  correspond  to  them.  This  culture  may 
be  repeated  ten,  twenty,  a  hundred,  even  a  thousand 
times :  in  the  latest  culture  the  virulence  is  not  ex- 
tinguished, or  even  sensibly  weakened.  But  it  is  a 
fact  worthy  of  attention  that  the  preservation  of  the 


222  LOUIS  PASTEUR. 

virulence  in  successive  cultures  is  assured  only  when 
no  great  interval  has  been  allowed  to  elapse  between 
the  cultures.  For  example,  the  second  culture  must 
be  sown  twenty-four  hours  after  the  first,  the  third 
twenty-four  hours  after  the  second,  the  hundredth 
twenty-four  hours  after  the  ninety-ninth,  and  so  on. 
If  a  culture  is  not  passed  on  to  the  following  one 
until  after  an  interval  of  several  days  or  several 
weeks,  and  particularly  if  several  months  have 
elapsed,  a  great  change  may  then  be  observed  in 
the  virulence.  This  change,  which  generally  varies 
with  the  duration  of  the  interval,  shows  itself  by  the 
weakening  of  the  power  of  the  contagium. 

If  the  successive  cultures  of  fowl  cholera,  made  at 
short  intervals,  have  such  virulence  that  ten  or  twenty 
inoculated  birds  perish  in  the  space  of  twenty-four 
or  forty-eight  hours,  a  culture  which  has  remained, 
say,  for  three  months  hi  its  flask,  the  mouth  of  which 
has  been  protected  from  the  introduction  of  all  foreign 
germs  by  a  stopper  of  cotton  wool,  which  allows 
nothing  but  pure  air  to  pass  through  it — this  culture, 
if  used  to  inoculate  twenty  fowls,  though  it  may 
render  them  more  or  less  ill,  does  not  cause  death  in 
any  of  them.  After  some  days  of  fever  they  recover 
both  their  appetite  and  spirits.  But  if  this  phenome- 
non is  extraordinary,  here  is  one  which  is  surely 
in  a  different  sense  singular.  If  after  the  cure  of 
these  twenty  birds  they  are  reinoculated  with  a  very 


THE   ATTENUATED   VIRUS,   OK  VACCINATION.     223 

virulent  virus — that,  for  instance,  which  was  just  now 
mentioned  as  capable  of  killing  its  hundred  per  cent, 
of  those  inoculated  with  it,  in  twenty-four  or  forty- 
eight  hours — these  fowls  would  perhaps  become  rather 
ill,  but  they  would  not  die.  The  conclusion  is  simple  ; 
the  disease  can  protect  from  itself.  It  has  evidently 
that  characteristic  of  all  virulent  diseases,  that  it 
cannot  attack  a  second  time. 

However  curious  it  may  be,  this  characteristic  is 
not  a  thing  unknown  in  pathology.  Formerly  it  was 
the  custom  to  inoculate  with  small-pox  to  preserve 
from  small-pox.  Sheep  are  still  inoculated  to  preserve 
them  from  the  rot ;  to  protect  horned  cattle  from 
peripneumonia  they  are  inoculated  with  the  virus  of 
the  disease.  Fowl  cholera  offers  the  same  immunity ; 
it  is  an  additional  scientific  acquisition,  but  not  a 
novelty  in  principle. 

The  great  novelty  which  is  the  outcome  of  the 
preceding  facts,  and  which  gives  them  a  distinct 
place  in  our  knowledge  of  virulent  diseases,  is  that  we 
have  here  to  do  with  a  disease  of  which  the  virulent 
agent  is  a  microscopic  parasite,  a  living  organism 
cultivated  outside  of  the  animal  body,  and  that  the 
attenuation  of  the  virulence  is  in  the  power  of  the 
experimenter.  He  creates  it,  he  diminishes  it,  he 
does  what  he  wishes  with  it ;  and  all  these  variable 
virulences  he  obtains  from  the  maximum  virulence 

by  manipulation  in  the  laboratory.     Looked  at  in 
12 


224  LOUIS  PASTEUE. 

juxtaposition  with  the  great  fact  of  vaccination  for 
small-pox,  this  weakened  microbe,  which  does  not 
cause  death,  behaves  like  a  real  vaccine  relatively  to 
the  microbe  which  kills,  producing  a  malady  which 
may  be  called  benign,  since  it  does  not  cause  death, 
but  is  a  protection  from  the  same  malady  in  its  more 
deadly  form. 

But  for  this  enfeebled  microbe  to  be  a  real  vaccine, 
comparable  to  that  of  cow-pox,  must  it  not  be  fixed,  so 
to  speak,  in  its  own  variety,  so  that  there  should  be 
no  necessity  for  having  recourse  again  to  the  pre- 
paration from  which  it  was  originally  derived? 
Jenner,  when  he  had  demonstrated  that  cow-pox 
vaccination  preserved  from  small- pox,  feared  for  some 
time  that  it  would  be  always  necessary  to  have 
recourse  to  the  cow  to  procure  fresh  vaccinating 
matter.  His  true  discovery  consisted  in  establishing 
that  the  cow-pox  from  the  cow  could  be  dispensed 
with,  and  that  inoculation  could  be  performed  from 
arm  to  arm.  Pasteur  made  his  enfeebled  microbe 
pass  from  one  cultivation  to  another.  What  would  it 
become  ?  Would  it  resume  its  very  active  virulence, 
or  would  it  preserve  its  moderate  virulence  ? 

The  virulence  remained  enfeebled  and,  we  may  say, 
unchanged.  This  showed  it  to  be  a  real  vaccine. 
Some  veterinary  surgeons  and  farmers,  on  the  an- 
nouncement of  this  discovery,  applied  to  Pasteur  for 
a  vaccine  against  the  disease  which  was  so  disastrous 


THE  ATTENUATED  VIRUS,   OR  VACCINATION.     225 

among  their  poultry.  Some  trials  were  made,  and 
all  succeeded  beyond  expectation.  To  preserve  this 
vaccine  it  must  be  secured  from  contact  with  the  air, 
the  cultures  being  enclosed  in  tubes,  the  extremities 
of  which  are  sealed  by  the  flame  of  a  blowpipe. 

What  takes  place  during  that  interval  of  time  in- 
tentionally placed  between  two  successive  cultivations 
of  the  cholera  microbe — that  interval  which  is  em- 
ployed in  effecting  the  attenuation  and  producing  the 
vaccine  ?  What  is  the  secret  of  this  result  ?  The 
agent  which  intervenes  is  no  other  than  the  oxygen 
of  the  air.  Here  is  the  proof.  If  the  cultivation  of 
this  microbe  is  carried  on  in  a  tube  containing  very 
little  air,  and  if  the  tube  is  then  closed  by  the  flame 
of  a  lamp,  the  microbe,  by  its  development  and  life, 
quickly  appropriates  all  the  free  oxygen  contained  in 
the  tube,  as  well  as  the  oxygen  dissolved  in  the  liquid. 
Thus,  completely  protected  from  contact  with  oxygen, 
the  microbe  does  not  become  sensibly  weakened  for 
months,  sometimes  even  for  years. 

The  oxygen  of  the  air,  then,  appears  to  be  the 
cause  of  modification  in  the  virulence  of  the  microbe. 

But  how,  then,  is  the  absence  of  influence  on  the 
part  of  the  atmospheric  oxygen,  in  the  successive  cul- 
tures which  are  practised  every  twenty-four  hours,  to 
be  explained  ?  There  is,  in  Pasteur's  opinion,  but  one 
possible  explanation ;  it  is  that  the  oxygen  of  the  air 
in  this  latter  case  is  solely  employed  in  the  life  of  the 


226  LOUIS  PASTEUR. 

microbe.  A  culture  has  a  duration  of  some  days ;  in 
twenty-four  hours  it  is  not  terminated.  The  air  which 
comes  in  contact  with  it  is  then  entirely  employed 
in  nourishing  and  largely  reproducing  the  microbe. 
During  the  longer  intervals  of  culture,  the  air  acts 
only  as  a  modifier,  and  at  last  there  arrives  a  moment 
when  the  virulence  is  so  much  weakened  as  to  become 
nil. 

This  very  extraordinary  fact  is,  then,  established 
that  the  virulence  may  be  entirely  gone  while  yet 
the  microbe  lives.  The  cultures  offer  the  spectacle  of 
a  microbe  indefinitely  cultivable,  yet,  on  the  other 
hand,  incapable  of  living  in  the  bodies  of  fowls,  and 
in  consequence  deprived  of  virulence.  May  not  this 
domesticated  microbe,  as  M.  Bouley  calls  it,  be  com- 
pared to  those  inoffensive  microbes  of  which  there 
are  so  many  in  nature  ?  May  not  our  common  mi- 
crobes be  those  organisms  which  have  lost  their  former 
virulence?  But  may  not  these  harmless  microbes, 
become  infectious  in  some  particular  circumstances  ? 
And  if  there  are  fewer  virulent  maladies  now  than 
there  were  in  times  past,  might  not  the  number  of 
these  maladies  again  increase  ? 

Questions  multiply  as  the  facts  relating  to  the 
attenuation  of  a  virus  suggest  inductions,  awaken 
ideas,  and  throw  new  lights  upon  a  problem  which, 
until  within  these  last  few  years,  has  remained  so 
obscure.  Formerly  it  was  believed  that  these  viruses 


THE   ATTENUATED   VIRUS,   OR  VACCINATION.     227 

were  morbid  entities.  A  virus  was  a  unity.  This 
opinion  has  still  its  declared  upholders.  According  to 
Pasteur  a  virus  has  different  degrees  of  virulence  ;  it 
can  pass  from  the  weakest  virulence  to  the  maximum. 
Modifying,  at  will,  the  virus  of  fowl  cholera-,  Pasteur 
inoculates  some  hens,  for  instance,  with  a  virus  too 
attenuated  to  protect  from  death,  but  which  neverthe- 
less is  effectual  in  securing  them  against  a  virus 
stronger  than  itself.  The  second  virus  will  preserve 
them  from  the  attacks  of  a  third  virus,  and  thus 
passing  from  virus  to  virus  they  end  by  being  gua- 
ranteed against  the  most  deadly  virulences.  The  whole 
question  of  vaccination  resolves  itself  into  knowing 
at  what  moment  a  certain  degree  of  virus  attenuation 
is  a  guarantee  of  protection  against  the  mortal  virus. 

It  seems  that  between  small-pox  and  cow-pox  facts 
of  a  similar  kind  take  place.  It  is  probable  that 
vaccination  rarely  gives  perfect  security  against  the 
infection  of  a  very  malignant  small-pox ;  moreover, 
during  epidemics  of  small-pox  many  persons  who  have 
been  previously  vaccinated  are  attacked,  and  some 
even  die  of  the  disease. 

As  regards  the  practice  of  vaccinating  fowls  against 
the  cholera  peculiar  to  them — which,  though  it  cer- 
tainly is  not  of  the  same  importance  as  human  vac- 
cination, is  a  scientifically  capital  fact — we  may  hope 
that  whatever  the  differences  of  receptivity  in  different 
races,  or  in  different  individuals  of  the  same  race, 


228  LOUIS  PASTEUK. 

there  will  be  found  vaccines  to  suit  them  all,  special 
care  being  taken  to  resort  to  the  employment  of  two 
successive  vaccines  of  unequal  power,  employed  after 
an  interval  of  ten  or  fifteen  days.  The  first  vaccine 
may  always  be  chosen  of  a  degree  of  weakness  which 
will  not  in  any  case  cause  death,  and  yet  of  sufficient 
strength  to  prevent  dangerous  consequences  from  the 
second  vaccine,  which  would  in  some  cases  be  fatal 
if  employed  at  once,  and  to  enable  it  to  act  as  a 
vaccine  against  the  most  virulent  virus. 

With  regard  to  the  preparation  of  vaccines,  and  the 
ascertaining  of  their  proper  strength,  it  is  necessary  to 
make  trials  upon  a  certain  number  of  fowls,  even  at 
the  risk  of  sacrificing  a  few  in  these  preliminary 
experiments.  Beyond  such  questions  of  manipula- 
tion there  remains  still  a  scientific  question.  How 
are  the  effects  of  vaccination  to  be  conceived  ?  What 
explanation  can  be  given  of  the  fact  that  a  benign 
disease  can  preserve  from  a  more  serious  and  deadly 
one  ?  Pasteur  long  sought  for  the  solution  of  this 
problem.  Without  flattering  himself  that  he  has  un- 
ravelled the  difficulty,  he  has  nevertheless  amassed 
facts  which,  amid  these  physiological  mysteries,  per- 
mit us  to  frame  a  hypothesis  which  can  satisfy  the 
mind.  Pasteur  believes,  for  example,  that  the  vaccine, 
when  cultivated  in  the  body  of  the  animal,  robs  the 
globules  of  the  blood,  for  example,  of  certain  material 
principles  which  the  vital  actions  take  a  long  time  to 


THE  ATTENUATED   VIEUS,   OR  VACCINATION.     229 

restore  to  the  system,  and  which  to  the  most  deadly 
contagium  is  a  condition  of  life.  The  impossibility 
of  action  of  the  progressive  virus  and  of  the  deadly 
virus  is  thus  accounted  for. 

When  Pasteur  communicated  to  the  Academy  of 
Sciences  these  important  and  unforeseen  facts,  they 
were  at  first  received  with  hesitation.  It  was  not 
without  some  surprise  that  the  word  vaccination, 
hitherto  exclusively  reserved  for  Jenner's  discovery, 
was  heard  applied  to  fowl  cholera.  At  the  Inter- 
national Medical  Congress  held  in  London  in  August 
1881,  Pasteur,  in  the  presence  of  3,000  doctors 
of  medicine  from  all  parts  of  the  world,  who  received 
him  with  an  enthusiasm  which  reflected  glory  on 
France,  justified  the  name  that  he  had  given  to  his 
prophylactic  experiments. 

'  I  have  lent,'  he  said,  '  to  the  expression  vaccina- 
tion an  extension  that  I  hope  science  will  consecrate, 
as  a  homage  to  the  merit  and  immense  services 
rendered  to  humanity  by  one  of  the  greatest  men  of 
E  ngland — Jenner. ' 

Still,  while  rendering  homage  to  the  sentiment 
which  induced  Pasteur  to  efface  himself  in  favour  of 
Jenner,  we  may  be  permitted  to  say  that  there  is  no 
likeness  between  the  two  discoveries.  Great  as  was  the 
discovery  of  Jenner,  it  was  but  a  chance  observation, 
which  had  no  ulterior  development ;  and  for  a  whole 
century,  medicine  has  not  been  able  to  derive  anything 


230  LOUIS  PASTEUR. 

froin  it  beyond  its  actual  application,  which  is  the  one 
result  achieved.  'Vaccination  is  vaccination,'  an 
opponent  of  Pasteur's,  who  was  driven  hard,  was 
obliged  to  say.  The  opponent  found  no  other  answer, 
and  he  could  not  have  found  any  other.  The  cow-pox 
is  a  malady  belonging  exclusively  to  a  race  of  animals. 
Man  can  only  observe  it ;  he  cannot  produce  it.  Sup- 
press cow-pox  and  there  will  be  no  more  vaccination. 
In  the  French  discovery,  on  the  contrary,  it  is  the 
deadly  virus  itself  which  serves  as  a  starting  point  for 
the  vaccine.  It  is  the  hand  of  man  which  makes  the 
vaccine,  and  this  vaccine  may  be  artificially  prepared 
in  the  laboratory,  in  sufficient  quantity  to  supply  all 
needs.  What  a  future  is  presented  to  the  mind  in  the 
thought  that  the  virus  and  its  vaccines  are  a  living 
species,  and  that  in  this  species  there  are  all  sorts  of 
varieties  susceptible  of  being  fixed  by  artificial  cultiva- 
tion !  The  genius  of  Jenner  made  a  discovery,  but 
Pasteur  discovered  a  method  of  genius. 

'  This  is  but  a  beginning,'  said  M.  Bouley  on  the 
day  when  Pasteur  announced  these  facts  to  the 
Academy  of  Sciences.  *  A  new  doctrine  opens  itself  in 
medicine,  and  this  doctrine  appears  to  me  powerful 
and  luminous.  A  great  future  is  preparing ;  I  wait 
for  it  with  the  confidence  of  a  believer  and  with  the 
zeal  of  an  enthusiast.' 


THE   VACCINE  OF  SPLENIC  FEVER. 

WE  have  seen  how  the  facts  have  been  established 
with  regard  to  the  microbe  of  fowl  cholera.  Immu- 
nity against  a  virulent  disease  may  be  obtained  by 
the  influence  of  a  benign  malady  which  is  induced  by 
the  same  microbe,  only  weakened  in  virulence.  What 
a  future  there  would  be  for  medicine  if  this  method 
could  be  applied  to  the  prevention  of  all  virulent 
diseases !  As  splenic  fever  was  at  that  time  being 
studied  in  the  laboratory  of  the  Ecole  Normale,  it  was 
upon  this  fever  that  the  research  was  first  attempted. 
But  the  success  of  this  research,  said  Pasteur,  can 
only  be  hoped  for  if  the  disease  is  non-recurrent.  It 
is  only  in  this  case  that  inoculation  with  the  weakened 
microbe  can  protect  from  the  deadly  splenic  fever. 
Unfortunately,  human  medicine  is  dumb  as  regards  this 
question  of  non-recurrence.  The  man  who  is  smitten 
with  malignant  pustule  rarely  recovers.  If  there  are 
any  cases  of  recovery — and  there  are  some  authentic 
ones — he  who  has  so  narrowly  escaped  death  could 
not  confidently  count  upon  his  chance  of  protection 


232  LOUIS  PASTEUR. 

from  the  disease  in  future.  In  order  to  acquire  such 
a  sense  of  security  he  would  have  to  expose  himself  to 
experiments  of  direct  inoculation,  which  he  would 
hardly  care  to  do.  Animals  alone  offer  the  possibility 
of  solving  this  problem.  Yet  it  is  not  to  all  species 
of  animals  that  we  can  have  recourse.  Every  sheep 
inoculated  with  splenic  fever  infection  is  a  sheep  lost ; 
but  the  ox  and  the  cow  have  more  power  of  resistance. 
Among  them  there  are  frequent  cases  of  cure.  An 
incident  occurred  which  enabled  Pasteur  to  push  very 
far  this  experimental  study. 

In  1879  the  Minister  of  Agriculture  appointed  him 
to  give  judgment  upon  the  value  of  a  proposed  mode 
of  cure  for  cows  smitten  with  splenic  fever,  which  had 
been  devised  by  M.  Louvrier,  a  veterinary  surgeon  of 
the  Jura.  Choosing  M.  Chamberland  as  his  assistant 
to  watch  the  application  of  M.  Louvrier's  remedy, 
Pasteur  instituted  a  series  of  comparative  experiments. 
Some  cows  were  inoculated,  two  and  sometimes  four 
at  a  time,  with  the  virulent  splenic  fever  virus.  Half 
of  these  cows  were  treated  by  M.  Louvrier's  method ; 
the  other  half  were  left  without  treatment.  A  certain 
number  of  the  cows  under  M.  Louvrier's  care  resisted 
'the  disease,  but  an  equal  number  of  those  not  under 
treatment  recovered  also.  The  inefficacy  of  the 
remedy  was  demonstrated  as  well  as  the  cause  of  the 
inventor's  illusions.  But  one  precious  result  remained 
from  the  trial  of  this  remedy.  Pasteur  and  Chamber- 


THE   VACCINE   OF  SPLENIC   FEVER.  233 

land  had  thus  at  their  disposition  several  cows  which 
had  recovered  from  splenic  fever,  and  which  had  ex- 
perienced in  their  attack  all  the  worst  symptoms.  At 
the  places  of  inoculation  enormous  swellings  were 
formed,  which  extended  to  the  limbs,  or  under  the 
abdomen,  and  which  contained  several  quarts  of 
watery  fluid.  The  fever  had  been  intense,  and  at  one 
time  death  had  appeared  imminent.  When  these 
cows  recovered  they  were  reinoculated  with  great 
quantities  of  virulent  virus.  Not  the  least  trace  of 
disease  showed  itself,  even  in  cases  where  the  inocula- 
tion was  performed  after  an  interval  of  more  than  a 
year. 

The  question  was  solved  ;  splenic  fever,  like  most 
of  the  virulent  diseases  which  it  has  been  possible  to 
study,  was  non-recurrent.  The  immunity  obtained 
has  a  long  duration.  With  that  valiant  ardour 
which  always  urges  him  on,  Pasteur  next  proposed 
to  examine  the  vaccine  of  splenic  fever.  In  view 
of  these  new  investigations,  which  would  require 
long  and  careful  labours,  and  which  necessitated  a 
certain  amount  of  medical  knowledge,  Pasteur  asso- 
ciated with  himself,  in  addition  to  M.  Chamberland, 
a  young  savant,  now  a  doctor  of  medicine,  M. 
Eoux. 

Following  the  rigorous  course  of  his  deductions, 
Pasteur  naturally  turned  to  the  oxygen  of  the  air  in 
his  attempts  to  modify  the  virulence  of  the  splenic 


234  LOUIS  PASTEUR. 

microbe.  But  a  difficulty  presented  itself  at  the  out- 
set. Between  this  microbe  and  the  microbe  of  fowl 
cholera  there  exists  an  essential  difference.  The 
microbe  of  fowl  cholera,  as  is  the  case  with  a  great 
number  of  microscopic  organisms,  reproduces  itself 
only  by  fission.  The  parasite  of  splenic  fever,  on 
the  contrary,  has  another  mode  of  generation ;  it 
forms  spores,  nothing  analogous  to  which  is  found 
in  the  microbe  of  cholera. 

In  the  blood  of  animals,  as  in  the  cultures  at  the 
beginning,  the  splenic  fever  microbe  appears  at  first 
in  transparent  filaments,  more  or  less  divided  into 
segments.  Up  to  that  point,  the  resemblance  between 
the  microbe  of  splenic  fever  and  the  microbe  of  cholera 
is  complete.  But  this  blood,  or  the  cultures  exposed 
to  the  free  contact  of  the  air,  instead  of  continuing 
this  first  mode  of  generation,  frequently  exhibit,  even 
in  the  course  of  twenty- four  hours,  spores  distributed 
more  or  less  regularly  along  the  length  of  the  fila- 
ments. All  around  these  corpuscles  the  matter  of  the 
filaments  is  absorbed,  in  the  manner  formerly  illustrated 
by  Pasteur  in  the  diagrams  of  his  work  on  the  diseases 
of  silkworms,  when  treating  of  the  bacilli  of  putrefac- 
tion. Little  by  little,  all  cohesion  between  the  spores 
disappears,  and  the  whole  collection  soon  forms  no- 
thing more  than  a  dust  of  germs.  But-  and  here  lies 
the  great  difficulty  which  experimenters  encountered 
in  applying  to  splenic  fever  the  method  of  gradual 


THE   VACCINE   OF  SPLENIC   FEVER.  235 

attenuation  which  was  practised  with  the  microbe  of 
cholera — these  germs  of  splenic  fever  may  be  exposed 
for  years  to  the  air  without  losing  their  virulence, 
always  ready  to  reproduce  themselves  without  any 
appreciable  change,  and  to  manifest  their  effects  in 
the  bodies  of  animals.  How  can  it  be  hoped  to  dis- 
cover a  vaccine  of  splenic  fever  by  the  method  used 
with  the  contagium  of  fowl  cholera,  since  the  splenic 
fever  virulence,  at  the  end  of  twenty-four  hours,  is  con- 
centrated in  a  spore  ?  Before  the  oxygen  of  the  air  has 
had  time  to  attenuate  the  contagium,  the  virulence  of 
the  parasite  would  be  encased  in  these  spores.  Yet 
this  objection  did  not  appear  insuperable  to  Pasteur. 
Since  (said  he  to  himself),  under  its  filamentous  form, 
the  microbe  of  splenic  fever  is  quite  analogous  to  the 
microbe  of  fowl  cholera,  may  not  the  problem  of  ex- 
posing the  splenic  microbe  to  the  air  be  reduced  to 
the  following  one  :  to  determine  the  conditions  which 
would  prevent  the  production  of  spores  ?  The  diffi- 
culty would  thus  be  surmounted ;  for,  once  we  have 
got  rid  of  the  spores,  the  splenic  filaments  might  be 
maintained  in  contact  with  air  for  any  length  of  time, 
and  we  might  then  no  doubt  fall  back  upon  the  con- 
ditions which  had  produced  the  attenuation  of  the 
cholera  microbe. 

Pasteur  and  his  two  assistants  gave  themselves  up 
to  this  research.  Days  passed  and  experiments  were 
multiplied.  Pasteur  became  more  and  more  en- 


236  LOUIS  PASTEUK. 

grossed :  he  had,  what  his  daughter  called,  '  the  face 
of  an  approaching  discovery.' 

'  Ah !  what  a  grand  thing  it  would  be,'  he  was 
heard  from  time  to  time  to  murmur  to  himself  with  a 
suppressed  voice,  '  if  one  could  arrive  at  that — if  the 
fact  that  the  attenuation  of  the  microbe  of  fowl 
cholera  proved  not  to  be  an  isolated  one  !  '  But  if 
anyone  ventured  to  ask  him  a  timid  question  as  to 
the  phase  his  experiments  were  going  through,  he 
would  reply,  '  No,  I  can  tell  you  nothing.  I  dare 
not  express  aloud  what  I  hope.' 

At  last  one  day  he  came  up  from  his  laboratory 
with  a  triumphant  face.  His  joy  was  such  that  tears 
stood  in  his  eyes.  I  have  never  seen  a  more  radiant 
expression  of  the  highest  and  most  generous  emotions 
than  emanated  from  his  countenance. 

'  I  should  never  console  myself/  he  said  while  em- 
bracing us,  '  if  a  discovery  such  as  my  assistants  and 
I  have  just  made  were  not  a  French  discovery.' 

And  with  the  clearness  which  is  the  charm  of  this 
powerful  mind,  he  related  to  us  the  most  recent  dis- 
coveries of  his  laboratory. 

In  neutralised  chicken  infusion  the  splenic  microbe 
can  no  longer  be  cultivated  at  a  temperature  of  44 
or  45  degrees.  Its  cultivation,  on  the  contrary,  is 
easy  at  42  or  43  degrees ;  and  in  these  conditions  the 
microbe  produces  no  spores.  At  this  latter  tempera- 


THE  VACCINE   OF  SPLENIC   FEVER.  237 

ture,  therefore,  and  in  contact  with  pure  air,  we  can 
maintain  a  culture  of  filamentous  parasites  of  splenic 
fever,  deprived  of  all  germs.  In  some  weeks  the  crop 
dies — that  is  to  say,  when  this  culture  is  sown  in  fresh 
broth  the  sterility  of  the  broth  remains  complete.  But 
during  the  preceding  days  life  exists  in  the  cultivating 
liquid.  If  after  two,  four,  six,  or  eight  days  of  ex- 
posure to  the  air  and  to  heat,  the  contagium  is  tried 
upon  animals,  its  virulence  is  found  to  be  continually 
changing  with  the  time  of  its  exposure  to  the  air, 
and,  consequently,  it  represents  a  series  of  attenuated 
contagia.  From  the  moment  when  the  formation  of 
the  spores  of  the  splenic  fever  bacillus  is  prevented, 
all  becomes  substantially  the  same  as  in  thd  case  of 
the  microbe  of  fowl  cholera.  Moreover,  as  in  the 
cholera  microbe,  each  of  these  states  of  attenuated 
virulence  can  be  reproduced  by  cultivation.  Finally, 
splenic  fever  not  being  recurrent,  each  of  these  splenic 
fever  microbes  constitutes  a  vaccine  for  the  more 
virulent  microbe. 

In  order  to  apportion  the  virulence  of  the  vaccine 
to  the  species  it  is  desired  to  vaccinate,  it  must  be 
tried  on  a  certain  number  of  individuals  of  the  same 
species.  If  some  vaccinated  animals  are  inoculated 
with  the  virulent  virus,  and  none  of  them  perish,  the 
vaccine  is  good.  Among  individuals  of  the  same 
species,  however,  the  difference  of  receptivity  is  in 
general  great  enough  to  make  it  prudent,  and  even 


238  LOUIS  PASTEUR. 

necessary,  to  have  recourse  to  two  vaccines,  one  weak 
and  the  other  stronger,  with  an  interval  of  from  12  to 
15  days  between  the  two  inoculations. 

It  was  on  February  28,  1881,  that  Pasteur  com- 
municated to  the  Academy  of  Sciences,  in  his  own 
name,  and  in  those  of  his  two  fellow  workers,  the 
exposition  of  this  great  discovery.  Loud  applause 
burst  forth  with  patriotic  joy  and  pride.  And  yet  so 
marvellous  were  these  results  that  some  colleagues 
could  not  help  saying,  '  There  is  a  little  romance  in 
all  this.'  All  this  reminds  one,  in  fact,  of  what  the 
alchemist  of  Lesage  did  to  the  demons  which  annoyed 
him.  He  shut  them  up  in  little  bottles,  well  corked, 
and  so  kept  them  imprisoned  and  inoffensive.  Pasteur 
shut  up  in  glass  bulbs  a  whole  world  of  microbes,  with 
all  sorts  of  varieties  which  he  cultivated  at  will.  Viru- 
lences attenuated  or  terrible,  diseases  benign  or  deadly, 
he  could  offer  all.  Hardly  had  the  journals  published 
the  compte-rendu  of  this  communication  when  the 
President  of  the  Society  of  Agriculture  in  Melun,  M. 
le  Baron  de  la  Eochette,  came,  in  the  name  of  the 
Socitey,  to  invite  Pasteur  to  make  a  public  experiment 
of  splenic  fever  vaccination. 

Pasteur  accepted.  On  April  28  a  sort  of  conven- 
tion was  entered  into  between  him  and  the  Society. 
The  Society  agreed  to  place  at  the  disposal  of  Pasteur 
and  his  two  young  assistants,  Chamberland  and  Koux, 


THE  VACCINE  OF  SPLENIC   FEVER.  289 

sixty  sheep.  Ten  of  these  sheep  were  not  to  receive 
any  treatment ;  twenty-five  were  to  be  subjected  to 
two  vaccinal  inoculations  at  intervals  of  from  twelve 
to  fifteen  days,  by  two  vaccines  of  unequal  strength. 
Some  days  later  these  twenty-five  sheep,  as  well  as 
the  twenty-five  remaining  ones,  were  to  be  inoculated 
with  the  virus  of  virulent  splenic  fever.  A  similar  ex- 
periment was  to  be  made  upon  ten  cows.  Six  were  to 
be  vaccinated,  four  not  vaccinated ;  and  the  ten  cows 
were  afterwards,  on  the  same  day  as  the  fifty  sheep,  to 
receive  inoculation  from  a  very  virulent  virus. 

Pasteur  affirmed  that  the  twenty-five  sheep  which 
had  not  been  vaccinated  would  perish,  while  the 
twenty-five  vaccinated  ones  would  resist  the  very 
virulent  virus ;  that  the  six  vaccinated  cows  would 
not  take  the  disease,  while  the  four  which  had  not 
been  vaccinated,  even  if  they  did  not  die,  would  at  least 
be  extremely  ill. 

As  soon  as  the  agricultural  and  scientific  press 
had  published  this  programme,  and  recorded  Pasteur's 
prophecies,  several  of  his  colleagues  at  the  Academy  of 
Sciences,  startled  by  such  boldness  in  reference  to  a 
subject  which  had  hitherto  been  enveloped  in  such 
profound  obscurity,  and  fearing  to  see  the  illustrious 
company  somewhat  compromised  by  these  affirmations 
in  relation  to  problems  of  physiology  and  pathology, 
addressed  some  observations  to  M.  Pasteur  on  what 
they  called  '  a  scientific  imprudence.' 


240  LOUIS  PASTEUR. 

'  Take  care,'  they  said  to  him,  '  you  are  commit- 
ting yourself  without  possibility  of  retreat.  Your 
experiments  in  the  laboratory  hardly  authorise  you  to 
attempt  experiments  like  those  at  Melun.' 

'No  doubt,'  Pasteur  answered,  'we  have  never 
had  in  our  experimental  studies  so  many  animals  at 
our  disposition  to  inoculate  ;  but  I  have  full  confi- 
dence. What  has  been  already  done  in  my  laboratory 
is  to  me  a  guarantee  of  what  can  be  done.' 

And  M.  Bouley,  confident  also  in  the  assurances 
of  his  illustrious  friend,  and  arranging  to  meet  him, 
to  witness  these  audacious  experiments,  said  to  his 
anxious  colleagues,  '  Fear  nothing  ;  he  will  come  back 
triumphant.' 

The  experiments  began  on  May  5,  1881,  at  four 
kilometers'  distance  from  Melun,  in  a  farm  of  the 
commune  of  Pouilly-le-Fort,  belonging  to  a  veterinary 
doctor,  M.  Eossignol,  secretary-general  of  the  Society 
of  Melun.  At  the  desire  of  the  Society  of  Agriculture, 
a  goat  had  been  substituted  for  one  of  the  twenty-five 
sheep  of  the  first  lot.  On  the  5th  of  May  they  inocu- 
lated, by  means  of  the  little  syringe  of  Pravaz — that 
which  is  used  in  all  hypodermic  injections — twenty- 
four  sheep,  the  goat,  and  six  cows  with  five  drops  of 
an  attenuated  splenic  virus.  Twelve  days  after,  on 
May  17,  they  reinoculated  these  thirty-one  animals 
with  an  attenuated  virus,  which  was,  however, 
stronger  than  the  preceding  one. 


THE  VACCINE  OF  SPLENIC  FEVEK.  241 

On  May  31  very  virulent  inoculation  was  effected. 
Veterinary  doctors,  inquisitive  people,  and  agricul- 
turists formed  a  crowd  round  this  little  flock.  The 
thirty-one  vaccinated  subjects  awaiting  the  terrible 
trial  stood  side  by  side  with  the  twenty-five  sheep 
and  the  four  cows,  which  awaited  also  their  first  turn 
of  virulent  inoculation.  Upon  the  proposal  of  a 
veterinary  doctor,  who  disguised  his  scepticism  under 
the  expressed  desire  to  render  the  trials  more  com- 
parative, they  inoculated  alternately  a  vaccinated  and 
a  non-vaccinated  animal.  A  meeting  was  then  ar- 
ranged by  Pasteur  and  all  other  persons  present  for 
Thursday,  June  2,  thus  allowing  an  interval  of  forty- 
eight  hours  after  the  virulent  inoculation. 

More  than  t\vo  hundred  persons  met  that  day  at 
Melun.  The  Prefect  of  Seine-et-Marne,  M.  Patinot, 
senators,  general  counsellors,  journalists,  a  great 
number  of  doctors,  of  veterinary  surgeons,  and 
farmers ;  those  who  believed,  and  those  who  doubted, 
came,  impatient  for  the  result.  On  their  arrival  at 
the  farm  of  Pouilly-le-Fort,  they  could  not  repress 
a  shout  of  admiration.  Out  of  the  twenty-five  sheep 
which  had  not  been  vaccinated,  twenty-one  were  dead ; 
the  goat  was  also  dead  ;  two  other  sheep  were  dying, 
and  the  last,  already  smitten,  was  certain  to  die  that 
very  evening.  The  non-vaccinated  cows  had  all  volu- 
minous swellings  at  the  point  of  inoculation,  behind 
the  shoulder.  The  fever  was  intense,  and  they  had 


242  LOUIS  PASTEUR. 

no  longer  strength  to  eat.  The  vaccinated  sheep  were 
in  full  health  and  gaiety.  The  vaccinated  cows 
showed  no  tumour ;  they  had  not  even  suffered  an 
elevation  of  temperature,  and  they  continued  to  eat 
quietly. 

There  was  a  burst  of  enthusiasm  at  these  truly 
marvellous  results.  The  veterinary  surgeons  especi- 
ally, who  had  received  with  entire  incredulity  the  an- 
ticipations recorded  in  the  programme  of  the  experi- 
ments, who  in  their  conversations  and  in  their  journals 
had  declared  very  loudly  that  it  was  difficult  to  believe 
in  the  possibility  of  preparing  a  vaccine  capable  of 
triumphing  over  such  deadly  diseases  as  fowl  cholera 
and  splenic  fever,  could  not  recover  from  their  sur- 
prise. They  examined  the  dead,  they  felt  the  living. 

'  Well,'  said  M.  Bouley  to  one  of  them,  '  are  you 
convinced?  There  remains  nothing  for  you  to  do 
but  to  bow  before  the  master,'  he  added,  pointing  to 
Pasteur,  'and  to  exclaim — 

"  I  see,  I  know,  I  believe,  I  am  undeceived."  ' 

Having  suddenly  become  fervent  apostles  of  the 
new  doctrine,  the  veterinary  surgeons  went  about 
proclaiming  everywhere  what  they  had  seen.  One 
of  those  who  had  been  the  most  sceptical  carried 
his  proselytising  zeal  to  such  a  point  that  he  wished 
to  inoculate  himself.  He  did  so  with  the  two  first 
vaccines,  without  other  accident  than  a  slight  fever. 


THE  VACCINE  0¥  SPLENIC  FEVER.  248 

It  required  all  the  efforts  of  his  family  to  prevent  him 
from  inoculating  himself  with  the  most  virulent  virus. 

An  extraordinary  movement  was  everywhere  pro- 
duced in  favour  of  vaccination.  A  great  number  of 
agricultural  societies  wished  to  repeat  the  celebrated 
experiment  of  Pouilly-le-Fort.  The  breeders  of  cattle 
overwhelmed  Pasteur  with  applications  for  vaccine. 
Pasteur  was  obliged  to  start  a  small  manufactory  for 
the  preparation  of  these  vaccines  in  the  Eue  Vauquelin, 
a  few  paces  from  his  laboratory.  At  the  end  of  the 
year  1881,  he  had  already  vaccinated  33,946  animals. 
This  number  was  composed  of  32,550  sheep,  1,254 
oxen,  142  horses.  In  1882,  the  number  of  animals 
vaccinated  amounted  to  399,102,  which  included 
47,000  oxen  and  2,000  horses.  In  1883,  100,000 
animals  were  added  to  the  total  of  1882. 

From  the  commencement  of  the  practical  appli- 
cation of  this  new  system,  the  results  were  topical. 
Among  flocks  where  half  had  been  vaccinated  and 
the  other  half  not  vaccinated — all  the  animals  con- 
tinuing to  live  together — the  mortality  from  splenic 
fever  in  1881  was  ten  times  less  in  the  vaccinated 
sheep  than  in  the  non-vaccinated,  being  1  in  740 
as  against  1  in  78 ;  and  in  cows  and  oxen  fourteen 
times  less,  being  1  in  1,254  against  1  in  88.  In  1882 
also,  the  mortality  was  ten  times  greater  among  the 
non- vaccinated  than  among  the  vaccinated  animals. 

In  1883  it  was  proved  that  the  duration  of  the 


244  LOUIS  PASTEUK. 

immunity  generally  lasted  longer  than  a  year.  It  is, 
however,  prudent  to  vaccinate  every  year,  and  to 
select  for  performing  the  operation  a  period  when 
splenic  fever  has  not  yet  become  developed — in  March 
and  April.  If  the  vaccinating  is  postponed  until  the 
fever  is  in  the  sheepfolds,  there  is  the  risk  of  attri- 
buting to  vaccination  the  losses  which  in  reality 
belong  to  the  natural  disease.  Just  as  human  vacci- 
nation cannot  preserve  from  small-pox  a  patient  who 
is  already  under  the  influence  of  small-pox,  so  the 
splenic  vaccinations  are  powerless  against  a  fever 
already  in  process  of  incubation. 

It  must  not  be  assumed  that  the  duration  of  im- 
munity to  animals  after  splenic  vaccination  cannot  be 
compared  with  the  duration  of  immunity  from  small- 
pox after  Jennerian  vaccination.  Jenner  and  his  con- 
temporaries believed  that  vaccination  was  able  to 
preserve  from  small-pox  during  the  whole  life.  That 
illusion  disappeared  long  ago,  and  now  ten  years  has 
been  fixed  as  the  average  duration  of  that  immunity 
and  of  the  interval  which  ought  to  separate  successive 
vaccinations.  This  interval,  moreover,  is  too  long  for 
a  certain  number  of  individuals.  Besides,  in  order  to 
judge  of  the  immunity  of  antisplenic  vaccination,  we 
must  not  lose  sight  of  the  formidable  trial  which 
vaccinated  animals  have  to  undergo  when  inoculated 
with  the  most  virulent  virus.  What  doctor  would 
dare  to  subject  a  vaccinated  child  to  inoculation  from 


THE  VACCINE  OF  SPLENIC   FEVER.  245 

virulent  small-pox  a  year  after  its  vaccination  ? 
Finally,  taking  into  consideration  the  commercial  and 
economic  view  of  the  life  of  a  sheep — if  such  an  ex- 
pression may  be  used — the  average  scarcely  exceeds 
three  years.  The  duration,  then,  of  the  immunity 
that  vaccination  confers  is  about  a  third  of  the  dura- 
tion of  the  animal's  life. 


246  LOUIS  PASTEUB. 


THE  RETURN   TO   VIRULENCE. 

AFTER  having  reduced  the  microbes  of  fowl  cholera 
and  splenic  fever  to  all  degrees  of  virulence,  and 
brought  them  to  a  point  where  they  could  no  longer 
multiply  in  the  bodies  of  animals  inoculated  with 
them,  and  fixed  them  in  media  appropriate  to  their 
life,  Pasteur  asked  himself  whether  it  would  not  be 
possible  to  restore  to  these  attenuated  microbes — 
weakened  to  such  a  degree  as  to  have  lost  all  viru- 
lence— a  deadly  virulence,  and  to  render  them  again 
capable  of  living  and  multiplying  in  the  bodies  o£ 
animals. 

Experiment  soon  confirmed  this  mental  previ- 
sion. An  attenuated  splenic  fever  virus  which  could 
cause  no  danger  of  disease  or  death  to  guinea-pigs  of 
a  year,  or  a  month,  or  even  a  week  old,  could  kill  a 
little  guinea-pig  just  born,  or  one  or  two  days  old. 
The  attenuated  microbe  could  multiply  itself  in  the 
blood  of  so  young  an  animal.  We  can  well  imagine 
that  in  an  animal,  scarcely  formed,  the  power  of  oxy- 
genation  of  the  blood  globules  is  not  as  yet  capable  of 


THE  KETUEN   TO   VIRULENCE.  247 

preventing  the  aerobic  microbe  from  turning  to  its 
own  account  the  oxygen  of  the  blood.  The  disease 
does  its  work  and  death  supervenes. 

After  all,  there  is  nothing  surprising  in  the  fact 
that  the  vital  resistance  of  a  newly-born  guinea-pig 
should  differ  from  that  of  an  adult  one.  But  what  is 
very  remarkable  is,  that  if  an  older  guinea-pig  be 
inoculated  with  the  blood  of  one  a  day  old  ;  if  a  third, 
still  older,  be  inoculated  with  the  blood  of  the  second  ; 
and  so  on  ;  the  virulence  of  the  microbe  will  be  gradu- 
ally reinforced — that  is  to  say,  the  usual  habit  of  this 
parasite  to  develop  itself  in  the  body  of  the  animal 
will  be  restored.  The  process  may  be  likened  to  that 
of  an  animal  or  vegetable  species,  passing  by  successive 
stages  and  long  sojourns,  from  one  region  to  another 
very  distant  one,  subjected  to  quite  new  conditions  of 
climate,  and  gradually  becoming  acclimatised  to  the 
last  one.  How  great,  then,  must  be  the  importance 
of  the  medium  of  cultivation,  with  regard  to  the  viru- 
lence of  the  microbes  of  communicable  diseases ! 
Cultivating  the  microbe  by  passing  it  from  one  guinea- 
pig  to  another,  we  soon  arrive  at  a  strength  capable 
of  killing  guinea-pigs  of  a  week,  a  month,  or  several 
years  old,  until  at  last  the  smallest  drop  of  the  blood 
of  these  guinea-pigs  suffices  to  kill  a  sheep ;  and  from 
the  sheep  we  may  pass  on  to  the  ox. 

The  same  is  the  case  with  the  microbe  of  fowl 
cholera.  When  it  has  ceased  to  have  any  effect  upon 
13 


248  LOUIS  PASTEUK 

fowls,  its  virulence  can  be  restored  by  inoculating 
small  birds.  Blackbirds,  canaries,  sparrows,  all  die, 
if  the  virus  has  not  been  too  much  attenuated ;  and 
the  effect  is  similar  on  young  chicks.  Thus  by 
several  successive  transitions  from,  bird  to  bird  a  viru- 
lence may  be  fostered  capable  of  destroying  full-grown 
fowls. 

These  facts  suggested  to  Pasteur  certain  inductions 
which  may  be  well  founded.  Is  not  the  attenuation  of 
the  virus  by  the  influence  of  the  air  one  of  the  factors 
in  the  extinction  of  great  epidemics  ?  And  may  not 
the  reappearance  of  these  scourges  be  accounted  for 
by  the  reinforcement  of  the  virulence  ? 

*  The  accounts  which  I  have  read,'  Pasteur  re- 
marked some  months  ago, '  of  the  spontaneous  appear- 
ance of  the  plague  in  Benghazi  in  1856  and  in  1858 
tend  to  prove  that  this  outbreak  could  not  be  traced 
to  any  original  contagion.  Let  us  suppose,  guided  by 
the  facts  now  known  to  us,  that  the  plagu6,  a  malig- 
nant disease  belonging  to  certain  countries,  has  germs 
of  long  duration.  In  all  these  countries  its  attenuated 
virus  must  exist,  ready  to  resume  its  active  form 
whenever  the  conditions  of  climate,  of  famine,  of 
misery  present  themselves  afresh.  The  condition  of 
long  duration  in  the  vitality  of  the  germs  of  evil  is 
not  even  indispensable;  for,  if  I  may  believe  the 
doctors  who  have  visited  these  countries,  in  all  places 
subject  to  the  plague,  and  in  the  intervals  of  the 


THE  RETURN  TO  VIRULENCE.  249 

great  outbreaks  of  the  epidemic,  cases  may  be  met 
with  of  people  attacked  with  boils,  not  fatal,  but 
resembling  those  of  the  deadly  plague.  Is  it  not  pro- 
bable that  these  boils  contain  an  attenuated  virus  of 
the  plague,  and  that  the  passage  of  this  virus  into  ex- 
hausted bodies,  which  abound  only  too  freely  in  periods 
of  famine,  may  restore  to  it  a  greater  virulence  ? 

*  The  same  may  be  the  case  with  other  maladies 
which  appear  suddenly,  like  typhus  in  armies  and  in 
camps.  Without  doubt,  the  germs  which  are  the 
authors  of  these  diseases  are  everywhere  scattered 
around,  but  attenuated ;  and  in  this  state  a  man 
may  carry  them  about  him  or  in  his  intestinal  canal 
without  great  damage.  They  only  become  dangerous 
when,  by  conditions  of  overcrowding,  and  perhaps  of 
successive  developments  on  the  surfaces  of  wounds,  in 
bodies  enfeebled  by  disease,  their  virulence  is  rein- 
forced.' 


250  LOUIS  PASTEUR. 


ETIOLOGY  OF  SPLENIC  FEVER. 

M.  PASTEUK  had  triumphed  over  splenic  fever  with  as 
much  rigour  as  precision.  But  he  considered  that  he 
had  still  to  make  one  further  investigation.  He  had 
established  the  effects  of  the  pest ;  he  had  discovered  a 
preventive  method  with  which  to  combat  it :  he  now 
wished  to  know  the  origin  of  the  evil.  Whence  comes 
splenic  fever  ?  Why  is  it  endemic  in  certain  depart- 
ments of  France,  in  certain  parts  of  Eussia,  Germany, 
Austria,  Italy,  Spain,  and  America  ?  How  is  it  sus- 
tained ?  It  was  for  a  long  time  believed  that  splenic 
fever  was  born  spontaneously  under  the  influence  of 
various  accidental  causes.  M.  Bouley  has  related,  in 
his  learned  work  on  the  '  Progress  of  Medicine  by 
Experimentation,'  that  in  1842  the  Minister  of  Agri- 
culture, M.  Cunin-Gridaine,  at  the  request  of  the 
deputies  of  the  departments  that  were  ravaged  by  the 
epidemic,  entrusted  to  M.  Delafond,  a  professor  of  the 
school  at  Alfort,  the  task  of  investigating  this  malady, 
commonly  called  the  '  blood  disease,'  in  the  districts  in 
which  it  was  raging.  He  was  to  search  out  its  causes, 


ETIOLOGY  OF  SPLENIC  FEVER.  251 

and  ascertain  whether  they  did  not  result  from  the 
system  of  cultivation  prevalent  in  the  country. 

M.  Delafond  arrived  in  Beauce.  One  fact  struck 
him — namely,  that  almost  all  the  animals  attacked  by 
the  disease  were  young,  fine,  and  vigorous :  those,  in 
short,  that  gave  the  best  promise.  Viewing  the  rich- 
ness of  the  soil  and  the  abundance  and  quality  of  the 
crops  in  conjunction  with  this  observation,  Delafond 
at  once  elaborated  a  speculative  theory.  '  The  blood 
disease,'  said  he,  '  is  nothing  but  an  overfulness — an 
excess  of  blood  circulating  in  the  vessels,  and  especially 
the  predominance  in  that  liquid  of  red  globules. 

Starting  from  this  idea,  his  one  object  was,  by 
means  of  logical  deduction,  to  trace  everything  to  this 
fundamental  error.  He  analysed  the  soil,  and  demon- 
strated to  what  extent  it  was  fitted  to  furnish  crops 
that  were  rich  and  abounding  in  nutritive  properties. 
He  analysed  the  plants.  He  then  complacently  re- 
ferred the  richness  of  blood  of  the  Beauce  sheep  to 
the  richness  in  nitrogenous  principles  of  the  substances 
on  which  they  were  fed.  He  examined  the  lesions  of 
the  diseased  animals,  and  concluded  that  they  were 
the  consequence  of  the  blood  containing  too  large 
a  proportion  of  the  organic  elements,  called  globules, 
fibrine,  albumen,  and  too  small  a  proportion  of  water. 

'  Reduce  the  proportion  of  nutritious  elements,'  he 
wrote  as  his  advice  to  the  agriculturists,  'mix  roots 
with  all  that  is  too  rich  in  nitrogenous  principles,  and 


252  LOUIS   PASTEUK. 

you  will  reduce  in  proportion  the  losses  caused  by  the 
excess  of  the  ultra-nutritious  substances  with  which 
you  supersaturate  your  cattle.' 

'  Such  is  the  very  logical  conclusion  to  which  Dela- 
fond  was  led,'  adds  M.  Bouley,  ridiculing  these  obser- 
vations, based  on  a  method  of  reasoning,  instead  of  on 
the  experimental  method.  '  And  as  a  fresh  proof  of  his 
theory  he  mentions  the  fact  that  the  disease  decreases 
as  you  descend  the  country  towards  the  Loire.  On 
the  right  bank  of  that  river—  in  Sologne,  for  instance, 
which  is  a  low,  sandy,  damp  district — blood  disease  is 
unknown.  In  the  arrondissements  of  Gien  and  Mont- 
argis  and  in  parts  of  those  of  Orleans  and  Pithiviers 
it  prevails  but  little.  There,  Delafond  imperturbably 
remarks,  the  soil  is  sandy  and  the  herbage  not  nearly 
so  rich  as  in  the  Beauce  plateau ;  and  there  the  blood 
disease  is  consequently  less  common.' 

When  we  consider  that  such  opinions  could  be 
written  unchallenged  only  forty  years  ago,  that  they 
could  even  borrow  a  scientific  character  from  the  in- 
spiration that  gave  them  birth,  we  can  see  the  pro- 
gress that  has  since  been  made,  and  can  realise  how 
great  were  the  obscurity  and  uncertainty  which  have 
been  dispelled  by  the  experimental  method. 

The  presence  of  a  parasite  having  been  brought  to 
public  notice  in  the  blood  of  animals  suffering  from 
splenic  fever,  at  the  very  time  when  Pasteur  had 
shaken  the  belief  in  spontaneous  generation,  people 


ETIOLOGY  OF  SPLENIC  FEVER.       253 

grew  accustomed  to  the  idea  that  the  stricken  animals 
might  have  contracted  the  germs  of  the  malady  from 
the  outer  world,  without  any  spontaneous  birth, 
strictly  so  called,  of  the  disease.  This  opinion  was 
strengthened  by  a  knowledge  of  the  spores  of  the  splenic 
bacillus.  Pasteur,  aided  by  Messieurs  Chamberland 
and  Roux,  commenced  experiments  with  a  view  to 
solving  this  difficult  etiological  question.  The  first 
experiments  took  place  in  the  fields  of  a  farm  at  the 
village  of  St.  Germain,  near  Chartres.  Several  groups 
of  sheep  were  fed  on  lucern  grass  which  had  been 
sprinkled  with  artificially-reared  splenic  fever  bacteria, 
or  with  their  germs  or  spores.  Although  all  the  sheep 
of  the  same  group  absorbed  an  immense  number  of 
the  spores  of  the  parasite,  many  survived,  even  after 
being  visibly  affected.  Those  that  died  showed  all  the 
symptoms  of  what  is  called  spontaneous  splenic  fever. 
The  period  of  incubation  lasted  as  long  as  eight  or  ten 
days,  although,  in  its  latter  stages,  the  disease  exhibited 
those  startling  features  which  have  caused  a  belief 
that  the  incubating  period  is  a  very  short  one — short, 
that  is  to  say,  for  those  conditions  of  contagion  where 
the  parasite  is  not  deposited  in  its  pure  state  under 
the  animal's  skin. 

But  if  prickly  plants  (notably  the  pointed  ends  of 
dried  thistle  leaves,  or  beards  of  barley  blades  cut 
into  little  bits  about  a  centimeter  in  length)  were 
added  to  this  infected  food,  the  mortality  increased  to 


254  LOUIS  PASTEUE. 

a  striking  extent.  On  examination  after  death,  the 
lesions  of  these  animals  were  found  to  be  similar  to 
those  observed  in  sheep  which  were  attacked  by  splenic 
fever  in  sheds,  or  which  died  of  the  disease  in  the 
open  fields. 

From  that  time  forward,  the  idea  which  had  been 
predominant  in  the  minds  of  Pasteur  and  his  fellow- 
workers  during  all  their  inquiries,  was  materially 
strengthened.  They  were  convinced  that  the  animals 
which  died  of  blood  disease  in  the  department  of  Eure 
et  Loire  had  been  infected  by  germs  or  spores  of  the 
splenic  microbe  contained  in  their  food ;  but  the 
question  remained,  Whence  came  these  germs  ? 

From  the  moment  when  all  belief  in  the  spon- 
taneous generation  of  the  parasite  is  rejected,  attention 
is  naturally  drawn  to  the  possible  consequences  which 
may  arise  from  burying  in  the  earth  animals  which 
have  died  of  splenic  fever.  In  the  greater  number  of 
cases,  when  the  knacker's  establishment  is  too  far  off 
and  the  dead  animal  is  of  little  value,  a  trench  is  dug 
on  the  spot,  at  a  depth  varying  from  half  a  meter  to  a 
meter.  If  the  animal  dies  in  a  field,  it  is  buried  where 
it  falls ;  if  it  dies  in  a  shed  the  body  is  carried  into  a 
neighbouring  field.  There  it  is  buried,  and  putrefac- 
tion sets  in ;  and  since  all  the  splenic  fever  filaments 
of  the  blood  are  destroyed  by  putrefaction,  it  was 
thought  that  no  dissemination  of  the  germs  of  splenic 
fever,  after  the  animal  had  been  buried,  could  occur. 


ETIOLOGY   OF  SPLENIC   FEVER.  255 

Pasteur  showed  that  this  opinion  rested  on  a  super- 
ficial observation.  Even  when  the  animal  is  not  cut 
up,  blood  spreads  itself  outside  of  the  body  in  more  or 
less  abundance.  Is  it  not  an  habitual  characteristic  of 
the  disease,  that  at  the  time  of  death  blood  issues  from 
the  nostrils  and  the  mouth,  and  that  the  urine  is  often 
bloody?  All  around  the  corpse,  therefore,  the  earth 
is  polluted  with  blood.  Moreover  it  takes  several 
days  for  the  splenic  fever  microbe  to  resolve  itself  into 
harmless  granulations  by  the  action  of  gases,  other 
than  oxygen,  which  putrefaction  generates.  During 
this  time,  the  excessive  inflation  of  the  dead  body 
causes  the  liquids  of  the  interior  to  issue  from  all  the 
natural  apertures.  How  often  also,  a  rent  in  the  skin 
or  the  tissues  increases  this  flow.  The  blood  and  other 
matters,  mixed  with  the  surrounding  aerated  soil,  are 
no  longer  in  the  conditions  of  putrefaction,  but  rather 
in  those  which  form  a  suitable  medium  of  cultivation 
for  the  microbe.  Experiments  confirmed  these  views. 
Adding  some  splenic  fever  blood  to  earth  sprinkled 
with  the  water  of  yeast,  or  with  urine,  at  summer 
temperature,  or  at  the  temperature  which  the  fer- 
mentation of  a  dead  body  keeps  up  around  it,  as  in  a 
dung  heap,  in  less  than  twenty-four  hours  the  splenic 
fever  filaments  deposited  with  the  blood  had  multiplied 
and  resolved  themselves  into  spores.  These  spores 
were  afterwards  found  in  their  state  of  latent  life, 
ready  to  germinate  and  to  communicate  splenic  fever, 


256  LOUIS  PASTEUR. 

after  remaining  in  the  earth  for  months,  and  even 
years. 

These  experiments,  curious  as  they  were,  were 
only,  so  to  speak,  laboratory  experiments.  It  was 
necessary  to  investigate  what  happened  in  the  open 
country  with  all  the  variations  of  dryness,  of  damp,  and 
of  cultivation.  A  happy  inspiration  came  to  Pasteur 
and  his  assistants.  They  had  buried  in  the  midst  of 
summer,  in  an  isolated  corner  of  the  farm  of  St.  Ger- 
main, near  Chartres,  a  sheep  which  had  died  of  natural 
splenic  fever,  and  of  which  they  had  made  the  autopsy. 
Ten  months  afterwards,  and  again  fourteen  months 
afterwards,  the  idea  occurred  to  them  of  collecting 
some  of  the  earth  from  this  grave.  After  having  ex- 
amined it,  and  established  the  presence  of  the  spores 
of  the  microbe,  they  produced,  by  the  inoculation  of 
guinea-pigs,  the  splenic  disease  and  death.  But  the 
circumstance  which  deserves  the  greatest  attention,  is 
that  the  same  experiment  was  successfully  made  with 
the  earth  on  the  surface  of  the  grave,  though  this  earth 
had  not  been  disturbed  during  the  interval.  Some 
experiments  were  afterwards  made  on  the  earth  of 
some  trenches  dug  in  a  meadow  of  the  Jura,  where 
some  cows  which  had  died  of  splenic  fever  had  been 
buried  at  a  depth  of  two  meters.  Two  years  after- 
wards, by  successive  washings  of  the  earth  on  the  sur- 
face of  the  graves,  deposits  were  extracted  which  at 
once  produced  splenic  disease.  At  three  trials  within 


ETIOLOGY   OF   SPLENIC   FEVER.  257 

these  two  years  the  same  surface  earths  produced 
splenic  fever,  while,  away  from  the  graves,  the  earth 
exhibited  nothing  of  the  kind.  Finally,  Pasteur  and 
his  assistants  proved  that  on  the  surface  of  the  earth 
which  covered  the  buried  animals,  the  germs  were  again 
found,  after  all  the  operations  of  ploughing,  sowing, 
and  reaping. 

But  how,  it  will  be  asked,  can  the  earth,  which  is 
so  powerful  a  filter,  allow  the  germs  of  microscopic 
organisms  to  rise  again  to  its  surface  ?  Is  one  not 
tempted  here  to  quote  Pasteur  against  himself,  since, 
in  his  joint  researches  with  M.  Joubert,  Pasteur  had 
proved  that  the  waters  of  springs  issuing  from  the 
earth,  even  at  a  shallow  depth,  are  entirely  free  from 
germs  ?  Such  waters,  nevertheless,  being  supplied 
from  the  earth's  surface,  which  is  constantly  washed 
by  rain,  the  effect  must  be  to  carry  down  the  finest 
particles  to  the  springs.  But  these  latter,  notwith- 
standing conditions  so  conducive  to  their  pollution, 
remain  perfectly  pure.  Can  there  be  a  better  proof 
that  earth  of  a  certain  thickness  will  arrest  all  solid  par- 
ticles, even  the  most  minute  ?  Nevertheless,  in  these 
experiments  on  splenic  fever,  we  hear  of  microscopic 
germs,  starting  from  the  depths  and  coming  up  to  the 
surface — that  is  to  say,  in  a  direction  contrary  to  the 
flow  of  the  rain.  This  is  an  enigma. 

The  explanation  will  cause  surprise.  The  earth- 
worms transport  the  germs,  and  "bring  up,  from  the 


258  LOUIS  PASTEUR. 

depths  where  they  lie  buried,  the  terrible  microbes.  In 
the  tiny  cylinders  of  earth  which  the  worms  deposit  on 
the  surface  of  the  soil,  after  the  dews  of  the  morning 
or  after  rain,  the  splenic  germs  are  to  be  found.  It  is 
easy  to  prove  this  directly.  If  in  earth,  with  which 
spores  of  the  microbe  have  been  previously  mingled, 
we  place  some  worms,  and  at  the  end  of  several  days 
open  the  bodies  of  these  worms,  with  all  necessary 
precautions,  so  as  to  extract  from  them  the  earthy 
matter  which  fills  their  intestinal  canals,  we  find  in 
them  large  numbers  of  splenic  fever  spores.  It  is,  then, 
absolutely  proved,  that  if  splenic  fever  germs  exist,  as 
they  often  do,  in  the  light  earth  which  covers  the  pits 
in  which  animals  dead  of  that  disease  lie  buried,  these 
germs  result  from  the  disintegration  by  rain  of  the 
little  excremental  cylinders  deposited  by  the  earth 
worms.  The  dust  of  this  disintegrated  earth  spreads 
itself  over  the  grasses  on  a  level  with  the  soil,  and 
thus  it  is  that  animals  come  to  find  on  the  pasture-field, 
and  in  particular  kinds  of  forage,  the  germs  of  splenic 
fever  by  which  they  are  infected. 

'  In  these  results,'  said  Pasteur  a  short  time  ago  at 
the  Academy  of  Medicine,  '  what  outlooks  are  opened 
to  the  mind  in  regard  to  the  possible  influence  of 
earths  in  the  etiology  of  diseases,  and  the  possible 
danger  of  the  earth  of  cemeteries  ! ' 

The  earth-worms  also  bring  to  the  surface  other 
germs,  which,  while  they  are  as  harmless  to  the 


ETIOLOGY  OF  SPLENIC  FEVER.        259 

worms  as  the  splenic  germs,  are  nevertheless  bearers 
of  diseases  to  which  animals  are  liable.  All  sorts  of 
germs  are  found  in  them,  and  the  germs  of  splenic 
fever  are  in  fact  always  associated  with  those  of  putre- 
faction and  septicaemia. 

'  And  now,'  concluded  Pasteur,  when  laying  before 
the  Academy  a  rapid  survey  of  the  etiology  of  splenic 
fever,  '  is  not  the  remedy  naturally  indicated  ?  We 
should  never  bury  animals  in  fields  destined  either 
for  cultivation,  for  forage,  or  for  sheep  pasture. 
When  it  is  possible  a  sandy  soil  should  be  chosen  for 
the  purpose,  or  any  poor  calcareous  soil,  dry,  and 
easily  desiccated — in  a  word,  soil  not  suited  to  the  ex- 
istence of  earth-worms.'  M.  Tisserand,  Director  of 
Agriculture,  has  remarked  that  splenic  fever  is  un- 
known in  the  region  of  the  Savarts  of  Champagne, 
although  it  is  surrounded  by  countries  invaded  by  the 
disease.  If  the  conditions  of  commerce  introduce 
splenic  fever,  it  is  but  a  passing  accident.  Must  not 
this  be  attributed  to  the  fact  that  in  these  poor  soils, 
such  as  that  of  the  camp  at  Chalons,  where  the  thick- 
ness of  arable  soil  is  only  from  4  to  5  inches,  superposed 
upon  chalk,  the  worms  cannot  live  ?  In  such  a  soil 
the  burial  of  a  splenic  fever  animal  will  give  rise 
to  great  quantities  of  germs,  which,  owing  to  the 
absence  of  earth-worms,  will  abide  in  the  depths  of  the 
soil  and  remain  harmless.  Finally,  it  has  been 


260  LOUIS  PASTEUK. 

proved  that  the  countries  subject  to  splenic  fever  have 
an  argillaceous-calcareous  soil,  and  that  the  disease  is 
unknown  in  schistose  and  granitic  soils.  The  contrast 
of  the  results,  in  relation  to  such  differences  of  soil,  is 
seen  sometimes  in  the  Department  of  the  Aveyron, 
between  the  right  and  left  side  of  one  and  the  same 
road  or  watercourse. 

May  we  not  now  in  all  confidence  assert  that,  if 
the  cultivators  choose,  splenic  fever  may  soon  be  a 
thing  of  the  past  among  their  animals,  their  shep- 
herds, and  among  the  butchers  and  the  tanners  of 
the  towns,  because  splenic  fever  and  malignant  pus- 
tule are  never  spontaneous  ?  The  disease  exists  only 
where  it  has  been  sown,  or  where  it  has  been  diffused 
by  the  unconscious  instrumentality  of  the  earth-worm. 

The  progress  of  vaccination  will  also  contribute  to 
the  disappearance  of  splenic  fever  ;  for  this  preventive, 
if  extensively  used,  as  there  is  no  doubt  it  will  be,  must 
end  by  establishing  a  race  of  domestic  animals  which, 
having  all  sprung  from  vaccinated  parents,  will  in  conse- 
quence be  more  resistent  to  the  disease  in  its  worst  form. 
It  will  be  with  them  in  relation  to  splenic  fever  as  it 
is  with  ourselves  in  relation  to  small-pox.  It  is  a  well- 
known  fact  that  the  ravages  of  small-pox  are  much 
less  considerable  in  our  days  than  when  it  first 
•  appeared  in  Europe.  It  is  difficult  not  to  attribute 
this,  at  least  in  part,  to  the  prevalence  of  vaccination. 

In  the  populations  where  small-pox  is  introduced 


ETIOLOGY   OF  SPLENIC   FEVER.  261 

for  the  first  time  it  has  an  exceptional  intensity. 
Some  months  ago  a  significant  fact  of  this  nature 
occurred  in  Paris.  A  whole  family  of  Esquimaux 
perished  from  small-pox  in  the  '  Jardin  d'Acclimata- 
tion.'  They  had  never  been  vaccinated,  nor  had  their 
ancestors.  They  were  new  to  the  attacks  of  small-pox, 
which  did  not  spread  beyond  them. 


262  LOUIS  PASTEUR. 


METHOD  OF  DISCUSSION  AND 
CONTRADICTIONS. 

EVERY  new  discovery  produces  a  revolution  in  general 
ideas ;  a  revolution  gladly  hailed  by  some,  but  opposed 
by  others  as  disturbing  their  habits  of  thought  and 
reasoning.  Those  also  who  are  thrown  out  in  their 
calculations,  while  engaged  in  working  out  a  problem 
in  any  way  similar  to  the  one  that  has  been  solved, 
too  often  atone  for  their  dilatoriness  by  furious  denial 
of  the  newly  asserted  truth.  The  great  fact  of  the 
attenuation  of  virus,  the  artificial  production  of  the 
vaccines  of  chicken  cholera  and  of  splenic  fever,  the 
importance  of  their  employment  for  the  preservation 
of  animals  from  these  diseases,  excited  throughout 
the  world  a  surprise  and  enthusiasm  which  passionate 
critics  soon  sought  to  disparage.  The  fiercest  attack 
was  from  Germany.  It  commenced  immediately  after 
Pasteur's  triumph  at  the  International  Congress  of 
Medicine  held  in  London  in  1881.  The  German 
doctor  Koch  and  his  colleagues,  MM.  Gaffki  and 


METHOD  OF  DISCUSSION  AND   CONTRADICTIONS.      263 

Lceffler,  published  in  Berlin,  in  the  report  of  the 
German  Sanitary  Office,  a  kind  of  scientific  tirade 
against  the  discovery  of  virus  vaccine,  and  the  possi- 
bility of  utilising  it  in  the  large  operations  of  cattle- 
breeding. 

At  the  London  Congress  Dr.  Koch  had  said  to 
a  French  physician  that  the  possibility  of  attenuating 
virus  was  a  thing  too  good  to  be  true.  The  whole 
question  was  therefore  reopened  by  Dr.  Koch  and  his 
disciples.  At  first  Pasteur  let  the  torrent  flow ;  but, 
not  being  the  man  to  give  way  before  an  adversary, 
he  at  last  declared  that  the  attacks  of  the  German 
savants  must  be  repelled  at  Berlin  itself.  Continual 
applications  for  splenic  vaccine  were  made  to  him  from 
different  parts  of  Germany.  M.  Pasteur  replied  that, 
seeing  that  the  discovery  was  so  formally  contested  in 
Prussia,  it  would  be  well,  before  sending  any  vaccine 
abroad,  to  institute  a  great  demonstrative  experiment, 
as  had  been  done  at  Pouilly-le-Fort. 

Dr.  Roloff,  head  of  the  Veterinary  School  of  Berlin, 
hastened  to  take  the  initiative,  by  an  application  to 
the  German  Minister  of  Agriculture.  The  minister  at 
once  nominated  a  Commission  to  follow  the  experi- 
ments in  vaccination  and  to  draw  up  a  report  for  the 
German  Government.  M.  Pasteur  entrusted  the 
conduct  of  the  vaccinations  to  his  new  colleague,  Louis 
Thuillier,  who  accepted  with  deep  and  silent  joy  the 
management  of  an  experiment  that  was  to  test  a 


264  LOUIS  PASTEUR 

French  discovery.  He  was  always  ready  for  anything, 
this  brave  Thuillier,  who  was  destined  to  die,  a  martyr 
to  the  cause  of  science,  in  the  full  promise  of  his  youth, 
and  in  the  full  hope  of  glory.  His  courage  and  his 
work  were  alike  great  and  silent.  In  the  laboratory 
he  would  spend  days,  even  weeks,  without  speaking, 
bent  over  his  microscope  with  tenacious  resolution, 
endeavouring  to  follow  Pasteur  in  all  his  investigations  : 
proud  to  live  near  his  illustrious  master,  happy  to  be 
his  disciple  and  to  be  loved  by  him  almost  as  a  son. 
What  a  vacancy  he  has  left  in  the  laboratory  !  What 
a  place  he  might  have  held  in  science  ! 

The  composition  of  the  German  Commission,  over 
which  M.  Beyer,  member  of  the  Superior  Council  of 
Government,  presided,  showed  clearly  the  importance 
attached  by  Germany  to  the  investigation  of  this 
French  discovery.  Among  its  members  was  the 
famous  Professor  Virchow. 

The  experiments  were  carried  out  on  the  estate 
of  Pakisch.  The  minutes  and  reports  of  the  Com- 
mission left  no  doubt  as  to  the  correctness  of  the  facts 
announced  by  Pasteur.  But,  as  the  negations  of  Dr. 
Koch  and  his  colleagues  embraced  questions  beyond 
that  of  the  prophylaxy  of  splenic  fever,  Pasteur  did 
not  rest  content  with  this  initial  success ;  he  sought 
for  a  fresh  opportunity  of  convincing  his  opponents. 
This  opportunity  occurred  in  September  1882,  when 
an  International  Hygienic  Congress  was  held  at 


METHOD   OF  DISCUSSION   AND   CONTRADICTIONS.      265 

Geneva.  Thither  went  Pasteur,  hoping  to  meet  Dr. 
Koch  at  the  sittings ;  and  he  was  not  disappointed. 
Dr.  Koch  wras  there,  surrounded  by  his  disciples. 
From  the  tribune  of  the  Congress,  Pasteur  refuted  his 
criticism,  exposed  his  errors,  and  challenged  him  to 
a  discussion  in  the  presence  of  competent  judges. 
There  was  an  instantaneous  salvo  of  applause,  and 
everyone  awaited  Dr.  Koch's  reply.  But  he  declined 
all  debate,  reserving  his  case  for  careful  and  deliberate 
statement  in  the  press. 

It  took  three  months  for  Dr.  Koch  to  bring  out  a 
small  pamphlet,  and  these  three  months  had  borne 
their  fruit.  The  discovery  of  the  attenuation  of  virus, 
which  had  been  so  vehemently  attacked  only  a  year 
before  in  the  report  of  the  Sanitary  Office,  wras  now 
extolled  by  Dr.  Koch  as  a  discovery  of  the  first  im- 
portance. Being,  however,  unwilling  absolutely  to 
stultify  himself,  he  continued  the  attack  by  denying 
its  efficacy  in  practical  agriculture. 

The  clear,  direct  style  of  argument,  which  goes 
straight  to  its  point,  was  invariably  adopted  by 
Pasteur. 

'  Contradictions  may  retard,  although  they  cannot 
ultimately  prevent,  the  recognition  of  truth,'  he  once 
remarked  to  me  when  walking  in  the  gardens  of  the 
Ecole  Normale  ;  '  that  is  why  it  is  so  important  to 
remove  the  obstacles  which  temporarily  clog  and 


266  LOUIS  PASTEUK. 

hamper  it.  In  scientific  discussions,  it  is  not  as  in 
politics,'  he  added  with  a  smile, '  where  demonstration 
is  often  difficult.  In  the  natural  sciences,  doctrines 
must  be  based  on  an  assemblage  of  results,  of  ob- 
servations, and  of  experiments.  If  a  doctrine  is 
challenged,  it  seldom  happens  that  its  truth  or 
falsehood  cannot  be  established  by  the  application 
of  some  crucial  test.  Even  a  single  experiment 
will  often  suffice  either  to  refute  or  consolidate  the 
doctrine.' 

Keviewing  the  labours  of  the  past  forty  years, 
Pasteur  then  called  to  mind  the  numerous  controver- 
sies in  which  he  had  been  engaged.  Not  only  had  he 
been  attacked  by  Pouchet  and  Joly  on  the  question  of 
spontaneous  generation,  by  Liebig  on  the  subject  of 
fermentation,  by  Germans  and  Italians  regarding  the 
attenuation  of  virus,  but  every  one  of  his  assertions 
had  been  met  with  such  passionate  opposition  that, 
from  sheer  weariness,  he  had  invariably  ended  by 
referring  the  matter  to  some  authorised  commission, 
only  asking  it  to  put  an  end  to  all  strife  by  coming  to 
some  definite  decision. 

The  upshot  was  at  times  somewhat  amusing.  For 
instance,  when  Pasteur  described  to  the  Academy  of 
Medicine  how,  simply  by  lowering  the  temperature  of 
a  hen,  he  had  made  her  susceptible  to  inoculation  with 
splenic  fever,  the  facts  were  at  once  denied  by  M. 
Colin,  a  professor  of  the  school  of  Alfort.  Pasteur 


METHOD  OF  DISCUSSION  AND  CONTEADICTIOXS.      267 

immediately  requested  that  a  commission  might  be 
named,  which  should  include  both  himself  and  his 
opponent  among  its  members.  This  was  on  a  Tuesday, 
one  of  the  Academy  days  of  sitting.  The  following 
Saturday,  in  presence  cf  the  whole  commission, 
Pasteur  produced  four  hens  that  had  died  of  splenic 
fever.  M.  Colin  himself  conducted  the  autopsy.  It 
was  clear  to  everyone  that  their  blood  was  full  of  the 
filaments  of  the  splenic  fever  parasite.  The  proces- 
verbal  was  drawn  up  and  signed  by  all  the  members 
of  the  commission,  necessarily  including  M.  Colin.  The 
following  Tuesday  it  was  read  at  the  sitting  of  the 
Academy.  To  cover  his  retreat  M.  Colin  now  contended 
that  the  hens  had  taken  splenic  fever  not  because  they 
had  been  subjected  to  a  chilling  process,  but  because, 
so  as  to  keep  them  in  the  water,  the  poor  creatures 
had  had  their  wings  and  feet  tied  to  planks.  This 
sentimental  objection  was  disposed  of  by  comparative 
experiments  that  had  been  made  on  hens  similarly 
tied  and  inoculated,  but  not  chilled.  The  latter  had 
in  no  case  taken  the  disease. 

At  the  Academy  of  Sciences,  some  days  later,  a  mine 
was  sprung  upon  Pasteur  by  a  posthumous  publica- 
tion of  Claude  Bernard's.  He  again  submitted  this 
abruptly  raised  question  to  the  decision  of  the 
Academy.  A  series  of  experiments  had  been  found 
among  Bernard's  papers,  having  as  their  object  the 
inauguration  of  a  new  method  of  spontaneously  gene- 


268  LOUIS  PASTEUR. 

rating  the  substance  which  causes  the  fermentation  of 
the  must  of  the  grape. 

'  I  will  start  for  the  Jura,'  said  Pasteur.  '  In  the 
midst  of  my  vineyard,  which,'  he  proudly  added,  '  is 
ten  meters  square,  I  will  cover  over  some  stocks  with 
an  improvised  frame.  These  stocks  will  go  on  living 
and  bearing  grapes,  which  will  ripen.  It  is  now  July. 
At  this  time  of  year,  as  I  have  already  declared,  the 
germs  of  the  cellules  which  form  the  ferment  of  the 
grape  in  the  vats  do  not  yet  exist,  either  on  the  green 
grapes,  on  the  bunches,  or  on  the  vine  leaves.  I  will 
envelop  the  bunches  of  the  stocks  that  are  under- 
neath the  frame  with  a  layer  of  cotton  wool  that  has 
been  raised  to  a  temperature  of  150  degrees  Centigrade. 
This  done,  I  will  come  back  to  Paris  with  the  keys  of 
the  frame  in  my  pocket,  not  returning  to  the  Jura  until 
the  vintage  season,  at  the  beginning  of  October.  I 
predict  to  the  Academy,  that  the  grapes  wrapped  in 
cotton  wool  under  the  frame,  and  which  will  have 
grown  ripe,  may  be  crushed  in  the  open  air,  and  that 
the  juice  coming  from  them  will  not  be  capable  of 
fermentation.' 

This  prediction  was  fulfilled.  In  October,  Pasteur 
returned  to  the  Jura,  plucked  off  several  of  these 
stocks,  laden  with  ripe  bunches,  and  brought  them 
with  the  utmost  care  to  Paris.  He  had  at  last  the 
satisfaction  of  depositing  them  intact  on  the  table  of 
the  Academy  of  Sciences.  He  then  invited  M.  Berthe- 


METHOD   OF  DISCUSSION  AND  CONTEADICTIONS.      269 

lot  (editor  of  Bernard's  pamphlet),  and  all  his  col- 
leagues, to  cut  off  as  many  bunches  as  they  pleased. 
'  Only  crush  them  in  contact  with  pure  air,'  said  he, 
'  and  I  defy  you  to  produce  fermentation.' 

How  often  was  Pasteur  obliged  to  return  to  facts 
already  proved,  not  only  at  the  Academy  of  Sciences, 
but  at  the  Academy  of  Medicine,  where  M.  Jules 
Guerin,  at  the  age  of  eighty,  challenged  him  to  a  duel 
as  his  scientific  ultimatum !  If  M.  Pasteur  at  times 
pleaded  his  cause  with  too  much  passion,  it  was  the 
passion  of  truth,  the  burning  desire  to  convince,  which 
lent  such  power  and  defiance  to  his  vibrating  voice. 
He  could  not  endure  his  work  to  be  attacked — not 
from  pride,  none  was  more  modest  than  he — but  from 
irritation  at  the  denial  of  positive  facts;  facts  of 
which  he  was  a  thousand  times  assured,  and  which 
all  the  world  might  verify.  No  one  now  remembers 
these  discussions.  Time  has  passed,  and  opposition 
has  been  overthrown.  It  has  been  granted  to  Pasteur 
to  see,  everywhere  around  him,  the  beneficent  results 
of  his  discoveries.  From  all  parts,  from  his  own  as 
well  as  from  foreign  countries,  such  proofs  of  admira- 
tion and  gratitude  have  been  showered  upon  him  as  are 
usually  granted  only  to  those  whose  death  has  atoned 
for  their  genius.  He  has  opened  up  such  sources  of 
wealth  to  industry  and  agriculture  that,  as  the  learned 
English  professor  Huxley  has  truly  said,  '  Pasteur's 
discoveries  suffice,  of  themselves,  to  cover  the  war 


270  LOUIS  PASTEUE. 

indemnity  of  five  milliards  of  francs  paid  by  France  to 
Germany.'  His  investigations  of  contagious  diseases 
have  revealed  immense  possibilities  in  prophylaxy. 
But  Pasteur  considered  these  marvellous  discoveries 
as  a  mere  beginning.  '  You  will  see,'  he  often  said, 
'  how  it  will  all  grow  by-and-by.  Would  that  my 
time  were  longer  ! ' 


THE   LABORATORY  OF  THE  ECOLE 
NORMALS. 


VARIOUS    STUDIES.       HYDROPHOBIA. 

SINCE  the  day  when  a  minister  told  Pasteur,  that 
there  were  not  1,500  francs  in  the  budget  to  allow- 
for  the  expenses  of  his  laboratory,  science  has  ob- 
tained a  little  more  consideration.  At  the  present 
time  she  has  nothing  to  complain  of :  her  sovereignty 
is  recognised ;  her  schools  are  becoming  palaces ; 
she  has  an  amply  sufficient  civil  list :  she  is  rich 
enough,  in  short,  to  pay  for  her  researches.  M. 
Pasteur's  laboratory  has  had  its  full  share  of  the 
well-bestowed  generosity  of  the  State.  The  municipal 
council  of  Paris  even  wished  to  attach  vast  depen- 
dencies to  this  laboratory.  The  old  garden  of  the 
ancient  College  Eollin  was  placed  at  the  disposal  of 
Pasteur ;  who  at  once  hastened  to  build  stables  for 
lodging  horses  attacked  by  glanders,  stalls  for  shelter- 
ing splenic  fever  sheep,  and  kennels  for  the  reception 
of  mad  dogs.  But,  while  taking  advantage  of  these 
hospitable  premises,  Pasteur  still  retained,  in  the 
14 


272  LOUIS  PASTEUE. 

basement  of  his  laboratory  in  the  Eue  d'Ulm,  a  whole 
population  of  animals  under  experiment.  Isolated  in 
round  cages  which  impart  some  sense  of  security,  are 
the  rabid  dogs ;  some  attacked  with  furious  madness, 
biting  their  bars,  devouring  hay,  uttering  doleful 
howls  which  those  who  have  once  heard  can  never 
forget;  others  carrying  the  germ  of  this  terrible 
disease,  still  fawning  with  a  humble  look  of  tenderness, 
as  if  imploring  attention.  Hens  and  chickens  pass 
their  heads  through  the  wooden  bars  of  their  coops. 
From  time  to  time  a  cock  from  the  bottom  of  his  den 
crows  '  a  gloomy  dawn.'  Babbits  eat  peaceably,  while 
little  families  of  guinea-pigs  cluster  together,  and  at 
the  least  alarm  utter  a  frightened  cry.  All  these 
animals  are  destined  to  be  shortly  inoculated.  Each 
morning  a  round  of  inspection  is  made  in  this  little 
hospital  of  condemned  animals.  The  dead  are  taken 
out,  carried  to  one  of  the  upper  rooms,  and  placed  on 
the  dissecting-boards. 

It  is  also  to  such  boards  that  living  animals  are 
fastened  when  it  is  necessary  to  experiment  upon 
them.  Certainly  when  one  sees  a  dog  lying  with  a 
forlorn  look,  its  feet  tied,  its  body  trembling  from 
fright,  on  the  -point  of  undergoing,  though  in  full 
health,  a  bloody  operation,  one  cannot  suppress  the 
feelings  of  pity.  But  a  single  visit  to  a  physiological 
laboratory  suffices  to  reveal  vivisection  in  its  only 


THE  LABORATOKY  OF  THE  ECOLE  NORMALE.     273 

and  true  light ;  that  of  the  interest  it  offers  to  science, 
and  the  results  it  may  have  in  store  for  the  benefit  of 
humanity.  Moreover,  in  Pasteur's  laboratory,  every 
dog  subjected  to  vivisection  is  chloroformed.  The  per- 
sons who  take  up  the  controversy  about  vivisection  are 
careful  that  the  outside  world  shall  see  only  the  suffer- 
ing and  anguish  of  the  animal,  where  the  solution  of  a 
problem  should  be  the  object  kept  in  view.  Would  the 
English  physiologist  Harvey  have  discovered  the  cir- 
culation of  the  blood,  if  he  had  not  practised  vivisection 
on  deer  in  the  park  of  Charles  I.  ?  Would  Claude 
Bernard  have  been  able,  without  vivisection,  to  demon- 
strate the  glycogenic  function  of  the  liver  ?  If  Pasteur 
had  not  sacrificed  some  fowls  and  sheep,  would 
the  great  scientific  fact  of  the  attenuation  of  virus 
have  been  discovered  ?  If  500  dogs  had  to  perish, 
what  would  that  be,  compared  with  the  discovery  to- 
morrow of  the  cause  of  hydrophobia,  and  of  the 
means  of  protecting  humanity  against  this  frightful 
scourge  ? 

On  one  occasion,  in  presence  of  a  large  assembly, 
Pasteur  made  an  experiment  on  atmospheric  oxygen. 
He  placed  under  a  glass  bell  a  bird,  which  in  a  short 
time,  after  having  consumed  the  oxygen  contained 
in  the  bell,  gathered  itself  up  into  a  ball,  opened  its 
beak,  and  shut  its  eyes,  as  if  it  were  going  to  die. 
At  this  moment  Pasteur  introduced  a  second  sparrow, 
which,  passing  directly  from  the  ordinary  air  into 


274  LOUIS  PASTEUR. 

the  bell,  without  any  gradual  preparation,  immedi- 
ately fell,  asphyxiated.  There  was  a  little  exclamation 
of  horror  and  a  movement  of  pity  in  the  audience. 
While  the  first  sparrow,  which  had  gone  through 
the  ordeal  unharmed,  was  set  free,  and  gradually 
revived,  Pasteur  turned  towards  the  assembly  and 
said — 

'  I  never  had  the  courage  to  kill  a  bird  in  sport, 
but  when  it  is  a  question  of  experiment  I  am  deterred 
by  no  scruple.  Science  has  the  right  to  assert  the 
sovereignty  of  its  aims.' 

But  to  return  to  the  animals  of  the  laboratory : 
From  the  little  white  mice,  which  hide  themselves  in  a 
packet  of  wadding,  to  the  dogs  which  bark  furiously 
in  their  iron  cages,  all  are  devoted  to  death.  But  it 
is  not  only  the  inmates  of  the  laboratory  which  daily 
succeed  each  other  upon  the  operating  and  dissecting 
tables.  From  divers  parts  of  France,  hampers  full  of 
fowls  which  have  died  of  cholera,  or  of  some  other 
disease,  are  sent  to  Pasteur.  Here  is  an  enormous 
basket  packed  with  straw  containing  the  dead  body 
of  a  pig  which  had  died  of  measles.  This  fragment 
of  lung,  packed  in  a  tin  box,  belonged  to  a  cow  which 
died  of  peripneumonia.  Other  packets  are  still  more 
precious.  Since  Pasteur  went  to  Pauillac  two  years 
ago,  to  watch  for  the  return  of  a  ship  which  was  to 
bring  back  eome  passengers  attacked  with  yellow 


THE   LABORATORY   OF   THE   ECOLE   SORMALE      275 

fever,  he  sometimes  receives  from  a  distant  country  a 
bottled  dose  of  vomito  negro. 

Everywhere,  on  the  work  tables,  are  to  be  seen  tubes 
filled  with  blood,  microscope  slides  carrying  little  drops. 
In  the  stoves  are  ranged  the  cultivating  flasks,  which 
resemble  little  flasks  of  liqueur.  The  point  of  a  needle 
dipped  into  one  of  these  flasks  is  sufficient  to  cause 
death.  Enclosed  in  their  glass  prison,  millions  upon 
millions  of  microbes  live  and  multiply. 

It  is  really  a  curious  spectacle  this  workshop  of 
research  and  discovery.  How  numerous  and  varied 
are  the  subjects  which  are  being  studied,  and  with 
what  energy  and  patience  does  Pasteur  attack  them  ! 
It  is  not  only  to  the  most  dreaded  diseases  that  he  has 
applied  the  germ  theory.  He  has  extended  it  to  certain 
common  disorders.  Everything  to  him  is  a  subject 
for  experiment.  In  May  1879,  a  person  who  was 
working  in  the  laboratory  was  troubled  with  boils, 
which  reappeared,  as  usually  happenb,  at  short  in- 
tervals, sometimes  on  one  part  of  the  body,  sometimes 
on  another.  Pasteur,  whose  mind  was  constantly 
dwelling  on  the  part  played  by  microscopic  organisms, 
asked  himself  if  the  pus  of  the  boils  did  not  contain 
a  parasite,  the  presence  and  development  of  which, 
.and  its  accidental  transport  here  and  there  in  the 
body,  might  be  the  cause  of  the  local  inflammation 
and  of  the  formation  of  the  pus.  The  constant  re- 
appearance of  the  evil  would  be  thus  accounted  for. 


276  LOUIS  PASTEUR. 

The  pus  of  the  first  boil,  which  was  situated  on  the 
nape  of  the  neck,  was  collected  in  great  purity ;  some 
days  afterwards,  the  pus  of  a  second  boil,  then  of  a 
third  boil,  was  collected.  The  pus,  or  the  blood- 
stained lymph  of  the  red  swelling  which  preceded  the 
formation  of  the  pus,  were  sown  in  a  sterilised  infusion, 
and  each  time  a  microbe,  formed  of  little  spherical 
points  connected  in  pairs,  frequently  united  in  small 
clusters,  was  seen  to  develop  itself.  The  cultivating 
liquid  was  sometimes  infusion  of  fowl,  sometimes  of 
yeast.  In  the  infusion  of  yeast  the  little  grains  are 
suspended  in  pairs  throughout  the  liquid,  which  is 
'Uniformly  thickened  with  them.  In  the  fowl  infu- 
sion, the  grains  are  united  into  little  clusters,  which 
cover  the  sides  of  the  vessels,  the  liquid  remaining 
clear  as  long  as  it  is  not  shaken. 

New  observations  were  made  upon  a  series  of 
boils,  in  the  case  of  a  man  sent  to  Pasteur  by  Dr. 
Maurice  Eaynaud.  The  same  parasite  was  again 
found — a  unique  parasite,  distinct  from  all  others.  At 
the  Hospital  Lariboisiere,  a  woman  whose  back  was 
covered  with  boils,  offered  another  opportunity  for  ex- 
periment, and  with  the  same  result.  It  appears  cer- 
tain, then,  that  every  boil  contains  a  microscopic 
aerobic  microbe,  and  that  to  it  are  due  the  local  in- 
flammation and  the  consequent  formation  of  pus. 

"When  guinea-pigs  or  rabbits  are  inoculated  with  the 
cultivating  liquids,  little  abscesses  are  formed,  which, 


THE  LABORATORY   OF  THE   ECOLE   NORMALS.     277 

however,  quickly  disappear.  As  long  as  the  cure  of 
these  little  abscesses  is  not  quite  completed,  one  can  ex- 
tract from  them  the  microscopic  organism  which  has 
formed  them.  When  the  little  parasite  is  sought  for  in 
the  general  blood  of  those  attacked  with  boils  it  is  not 
found.  The  cause  of  this,  no  doubt,  is  that  an  aerobic 
parasite  has  always  some  difficulty  in  developing  itself 
in  the  blood.  The  blood  corpuscles  appropriate,  and 
do  not  willingly  give  up  to  a  foreign  organism,  the 
oxygen  which  they  require.  There  is  a  struggle  for 
life,  and  in  the  struggle  against  the  boils  the  victory 
is  not  doubtful.  It  might  be  thought,  then,  that  the 
little  organism  of  boils  does  not  exist  in  the  blood,  but 
there  is  no  doubt  that  if,  instead  of  a  small  drop  of 
blood,  one  could  put  several  grammes  or  more  into 
cultivation  fruitful  results  would  follow.  The  little 
parasite  is  no  doubt  conveyed  by  the  blood  at  one  time 
or  other.  It  is  transported  from  a  boil,  in  the  process 
of  development,  to  another  point  of  the  body,  where  it 
may  be  fortuitously  arrested,  there  to  cultivate  itself 
and  form  a  new  boil. 

'  It  is  to  be  wished,'  said  Pasteur,  '  that  a  patient 
would  submit  to  a  number  of  punctures  on  different 
parts  of  the  body,  distant  from  boils  already  formed 
or  in  process  of  formation,  and  that  with  the  blood 
thus  taken  from  the  general  circulation  a  multitude  of 
cultivations  might  be  carried  on.  I  am  persuaded,' 
he  added,  '  that,  among  these  cultivations,  wre  should 


278  LOUIS  PASTEUK. 

find    some   fruitful    in    the   little   organism   of    the 
boils.' 

But  whilst  Dr.  Maurice  Raynaud  gave  Pasteur  the 
means  of  studying  boils,  Dr.  Lannelongue  enabled  him 
to  investigate  that  serious  disease  of  the  bones  and 
marrow  called  'osteomyelitis.'  In  February  1880 
that  skilful  surgeon,  who  has  published  a  highly 
esteemed  work  on  osteomyelitis,  and  on  the  possi- 
bility of  its  cure  by  trepanning  the  bone,  followed  by 
washings  and  antiseptic  dressings,  conducted  Pasteur 
to  the  Hospice  Trousseau.  A  little  girl  twelve  years 
of  age,  attacked  with  this  cruel  malady,  was  about  to 
be  operated  upon.  The  right  knee  was  much  swollen, 
as  was  also  all  the  leg  to  below  the  calf,  and  a  part 
of  the  thigh  above  the  knee.  After  having  chloro- 
formed the  child,  Dr.  Lannelongue  made  a  long  in- 
cision below  the  knee,  from  which  pus  flowed 
abundantly.  The  bone  of  the  tibia  was  laid  bare  for 
a  considerable  length.  Three  trepanning  perforations 
were  then  made  in  the  bone,  from  each  of  which  the 
pus  issued  in  great  quantities.  Pasteur  carefully 
collected,  with  all  the  conditions  necessary  to  the  pre- 
servation of  their  purity,  the  pus  of  the  exterior  and 
the  pus  of  the  interior  of  the  bone,  and,  returning  to 
his  laboratory,  he  examined  them  attentively.  The 
direct  observation,  by  a  microscope,  of  the  two  speci- 
mens of  pus  was  extremely  interesting.  It  was  obvious 
that  they  contained,  in  large  quantities,  an  organism 


THE  LABORATORY  OF  THE  ECOLE  NORMALS.     279 

like  that  of  boils,  in  pairs  of  two  or  four,  and  also  in 
parcels,  some  with  a  clearly  defined  outline,  others 
scarcely  visible,  and  with  very  faint  outlines.  The 
external  pus  showed  an  abundance  of  pus  globules, 
but  that  of  the  interior  did  not  show  any.  It  was 
like  a  paste  entirely  composed  of  microbes,  so  numerous 
and  fertile  that,  in  less  than  six  hours  after  sowing  them 
in  the  cultivating  liquid,  the  development  of  the  little 
microbe  had  commenced,  and  was  rendered  visible  to 
the  naked  eye  by  a  slight  but  general  turbidity  of  the 
liquid. 

Its  close  resemblance  to  the  organism  of  the  boil 
might  lead  to  the  assertion  that  they  are  identical,  if 
it  were  not  known  how  great  are  the  physiological 
differences  that  may  exist  between  microscopic  parasites 
of  the  same  appearance  and  the  same  dimensions. 

I. 

As  Pasteur  advanced  in  these  studies,  he  found  at 
the  Academy  of  Medicine  some  fellow  labourers,  who 
being  keenly  interested  in  such  researches  did  all  they 
could  to  promote  them.  Thus  M.  Villemin,  the  chief 
medical  officer  of  the  Val  de  Grace  (who  had  with  so 
much  sagacity  discovered  the  contagion  of  tuber- 
culosis) when  typhoid  fever  was  raging  in  Paris  two 
years  ago,  never  allowed  a  case  of  the  fever  to  pass 
through  his  hands  without  informing  Pasteur,  who 


280  LOUIS   PASTEUR. 

habitually  went  himself  to  collect  specimens  of  the 
blood  of  those  who  had  died.  How  numerous  were  the 
drops  of  blood  thus  enclosed  in  little  tubes,  and  how 
frequent  the  attempts  at  cultivation,  as  yet  without  re- 
sult, in  the  hope  of  finding  the  cause  of  a  disease  which 
claims  so  many  victims  !  There  is  another  malady  to 
which  Dr.  Hervieux  especially  called  Pasteur's  atten- 
tion, and  by  which  so  many  women  are  attacked — 
puerperal  fever.  He  went  with  M.  Hervieux  to  the 
Maternity  Hospital,  to  visit  a  woman  under  his  charge 
who  had  contracted  puerperal  fever  some  days  after  her 
confinement.  By  means  of  a  pin  a  prick  was  made  in 
the  forefinger  of  the  left  hand,  which  had  been  washed 
previously  with  dilute  alcohol  and  carbolic  acid,  and 
dried  with  singed  linen.  The  drop  of  blood  taken 
in  this  way  was  sown  in  an  infusion  of  fowl.  For 
some  days  the  cultivation  remained  sterile.  Next 
day  blood  was  taken  from  a  fresh  puncture,  and 
this  time  it  proved  fertile.  The  woman  died  three 
days  after.  The  blood,  therefore,  already  at  the  time 
when  Pasteur  had  taken  it,  three  days  at  least  before 
death,  contained  a  microscopic  parasite  capable  of 
cultivation.  Eighteen  hours  before  this  woman  died, 
some  blood  taken  from  the  left  foot  had  been  sown, 
and,  like  the  former,  it  had  proved  productive  ;  but 
— and  this  fact  deserves  to  be  noted — Awhile  the  first 
productive  cultivation  only  contained  a  microbe  re- 
sembling that  of  boils,  the  other  cultivation  contained 


THE  LABORATORY  OF  THE  ECOLE  NORMALE.      281 

long  flexible  chaplets  clustered  together  like  tangled 
strings  of  beads. 

At  the  post-mortem  examination  of  this  woman 
large  quantities  of  pus  were  found  in  the  peritoneum 
and  the  uterus.  This  pus  was  sown  with  all  due  pre- 
caution. Some  blood  taken  from  the  basilic  and 
femoral  veins  was  likewise  sown.  It  was  everywhere 
easy  to  recognise  the  long  chaplets  in  little  tangled 
parcels,  and  always  without  admixture  of  other 
organisms,  except  in  the  cultivation  of  the  perito- 
neal pus,  which,  besides  the  long  strings  of  grains, 
showed  also  the  little  pyogenic  vibrios  to  which  Pasteur 
had  already  assigned  the  name  of  the  pus  organism. 

From  the  Maternity  Hospital  Pasteur  went  to  the 
Hopital  Lariboisiere,  where  he  had  been  informed 
that  another  woman  had  just  died  of  the  same  fever. 
From  a  puncture  in  the  peritoneum  he  collected  some 
pus  which  was  found  there  in  great  abundance.  He 
sowed  this,  as  well  as  some  blood  taken  from  a  vein  in 
the  arm.  The  culture  of  the  pus  furnished  the  long 
strings  of  grains  and  the  little  pyogenic  vibrio.  The 
culture  of  the  blood  exhibited  only  the  long  strings 
quite  pure. 

Pasteur  made  many  other  observations  of  the 
same  kind  in  cases  of  puerperal  fever.  He  arrived  at 
the  conclusion  that,  under  the  name  of  puerperal  fever, 
diseases  of  different  symptoms  were  classed,  but  which 
all  appear  to  be  the  result  of  the  invasion  of  common 


282  LOUIS  PASTEUR. 

organisms,  which  develop  themselves  on  the  surface  of 
wounded  parts,  and  from  thence  spread  themselves, 
in  one  form  or  another,  by  the  medium  of  the 
blood  or  of  the  lymphatics,  over  different  parts  of 
the  body.  Here  the  various  morbid  symptoms  are 
determined  by  the  nature  of  the  parasite  and  the 
general  constitution  of  the  patient.  Pasteur  is  con- 
vinced that,  with  the  possible  exception  of  cases 
where,  by  the  presence  either  of  internal  or  external 
abscesses,  the  body,  before  confinement,  contains 
microscopic  organisms,  the  antiseptic  treatment  ought 
to  be  infallible  in  preventing  puerperal  fever  from 
declaring  itself.  The  employment  of  carbolic  acid 
may  be  of  great  service ;  but  its  smell,  and  often  the 
melancholy  association  of  ideas  which  it  awakens, 
might  render  it  unsuitable  for  women  in  labour. 
There  is  not  the  same  objection  to  concentrated 
solutions  of  boric  acid,  which,  at  the  ordinary  tem- 
perature, contain  from  thirty  to  forty  grammes  of  acid 
to  one  litre  of  water. 

'Would  it  not  be  very  useful,' said  Pasteur  one 
day,  when  developing  his  ideas  and  observations  before 
the  Academy  of  Sciences,  '  to  place  always  by  the  bed- 
side of  each  patient  the  concentrated  and  wTarm  solu- 
tion of  boric  acid,  with  compresses  to  be  very  fre- 
quently renewed,  after  having  been  soaked  in  the 
solution,  these  applications  being  begun  immediately 
after  the  confinement  ?  It  would  also  be  prudent,  before 


THE   LABORATORY  OF   THE  ECOLE  NORMALE.     283 

using  the  compresses,  to  put  them  into  a  hot-air  stove, 
at  a  temperature  of  150  degrees,  which  is  more  than 
sufficient  to  kill  all  the  germs  of  common  organisms. 

I  have,'  he  added,  '  represented  the  facts  as  they 
have  appeared  to  me,  and  I  have  hazarded  the  interpre- 
tation of  them  ;  but  I  do  not  disguise  from  myself  that, 
in  the  domain  of  medicine,  it  is  difficult  to  withdraw 
oneself  entirely  from  a  pre-existing  subjective  bias; 
neither  do  I  forget  that  the  medical  and  veterinary 
studies  are  foreign  to  myself:  therefore  I  earnestly 
desire  judgment  and  criticism.  While  I  am  little 
tolerant  of  frivolous  contradiction  or  of  prejudice, 
despising  as  I  do  that  vulgar  scepticism  which  would 
erect  doubt  into  a  system,  I  honour  that  militant 
scepticism  which  makes  doubt  the  basis  of  a  method, 
whose  motto  is  "  More  light."  ' 

Since  these  ideas  have  penetrated  further  into 
practice ;  puerperal  fever,  I  was  told  lately  by  a  dis- 
tinguished medical  man,  is  hardly  known  in  the 
Maternity  Hospital.  The  employment  of  a  solution 
of  one  to  a  thousandth  of  corrosive  sublimate,  which 
is  one  of  the  best  antiseptics,  gives  excellent  results, 
and  keeps  off  all  danger.  May  it  not  be  permitted 
to  hope  that  puerperal  fever  will  soon  disappear 
in  the  same  way  that  purulent  infection  has  disap- 
peared in  hospitals,  since  the  introduction  of  Lister's 
dressings  ? 


284  LOUIS  PASTEUK. 


II. 

In  1882,  a  new  malady  occupied  the  attention  of 
the  laboratory  of  the  Ecole  Normale,  a  malady  the 
name  of  which  was  not  even  known  in  Paris,  but 
which  made  great  ravages  in  the  country — namely, 
swine  fever  (rouget).  Here,  again,  it  is  a  microbe 
which  causes  the  disorder.  This  microbe  was  first 
perceived  by  Thuillier,  in  a  little  commune  of  the  De- 
partement  de  Vienne,  when  examining  the  blood  and 
humours  of  pigs  which  had  died  of  the  fever.  Ex- 
periments were  at  once  set  on  foot  in  the  laboratory, 
with  the  view  of  proving  that  the  microbe  was  really 
the  cause  of  the  disease.  The  microbe  was  cultivated 
in  a  sterilised  infusion  of  veal.  This  cultivation  was 
passed  on  to  a  succeeding  one,  a  small  drop  of  the 
preceding  cultivation  being  always  taken  for  seed. 
Inoculations  from  these  last  cultivations  produced  the 
fever  in  certain  breeds  of  pigs.  The  proof  was  thus 
given  that  the  microbe  was  really  the  origin  of  the 
disease. 

Pasteur  then,  accompanied  by  Thuillier  and  a 
young  assistant,  M.  Loir,  went,  in  his  turn,  to  study 
the  disease  in  the  Department  of  Yaucluse.  He  re- 
mained more  than  a  month  in  the  canton  of  Bollene, 
in  the  house  of  a  veterinary  surgeon,  M.  Maucuer, 
who  took  him  to  all  the  pigsties  in  the  arrondissement. 


THE  LABORATORY  OF  THE  ECOLE  NORMALS.     285 

After  having  had  recourse  to  the  oxygen  of  the  air  to 
attenuate  the  virulence  of  the  microbe,  Pasteur  made 
some  experiments  in  vaccination.  Some  pigs  which 
had  been  vaccinated  remained  in  the  canton  of  Bol- 
lene, under  the  supervision  of  M.  Maucuer,  the 
owners  having  pledged  themselves  to  keep  their 
vaccinated  pigs  for  at  least  a  year.  In  the  ensuing 
September,  when  swine  fever  raged  everywhere  in  the 
canton  of  Bollene  and  in  the  arrondissement  of  Orange, 
not  a  single  vaccinated  pig  was  attacked.  '  They  are  all 
flourishing,'  wrote  M.  Maucuer.  An  address  of  thanks 
was  sent  to  Pasteur  by  the  municipal  council  of 
Bollene. 

But,  notwithstanding  these  happy  results,  the 
question  of  the  application  of  vaccines  to  different 
breeds  requires  still  further  investigation,  before  the 
vaccination  of  pigs  can  become  general. 

Soon  afterwards  a  method,  different  from  that  of 
the  atmospheric  oxygen,  for  weakening  the  virulence  of 
the  fever  virus,  was  tried  in  the  laboratory. 

Pasteur  had  proved  that  viruses  are  not  morbid 

entities,  that  they  can  assume  numerous  forms,  and 

• 
especially  physiological  properties,  dependent  on  the 

medium  in  which  they  live  and  multiply.  The  viru- 
lence belongs  to  living  microscopic  species,  but  is  at 
the  same  time  essentially  modifiable.  It  may  be 
weakened  or  intensified,  and  each  of  these  states  is 
capable  of  being  made  permanent  by  culture."  A 


286  LOUIS  PASTEUR. 

microbe  is  virulent  in  an  animal,  when  it  has  the 
power  of  swarming  in  the  body  of  that  animal,  after 
the  manner  of  a  parasite,  and  of  producing,  by  the  re- 
newal of  its  own  life,  disturbances  which  cause  disease 
and  death.  If  this  microbe  has  lived  in  any  species 
of  animal — that  is  to  say,  if  several  times  over  it  has 
passed  from  the  body  of  one  individual  into  that  of 
another  of  the  same  kind,  without  having  been  sub- 
jected to  any  sensible  exterior  influence  during  its 
passage — we  may  consider  that  the  virulence  of  this 
parasite  has  reached  a  fixed  and  maximum  state  for 
the  individuals  of  that  race.  The  splenic  fever  para- 
site pertaining  to  sheep,  for  instance,  varies  little 
from  one  subject  to  another  or  from  one  year  to 
another  in  the  same  country ;  this  must  be  attributed, 
doubtless,  to  the  fact  that,  in  its  successive  passages 
through  the  sheep,  the  habit  of  the  parasite  to  live  hi 
sheep  has,  so  to  speak,  attained  a  definite  state.  It  is 
thus  with  the  virus  of  the  Jennerian  vaccination.  But 
the  virulence  of  a  virus  which  is  not  at  its  maximum 
may  be  essentially  modified  by  its  passage  into  a 
succession  of  individuals  of  the  same  race.  It  will  be 
remembered  how,  when  Pasteur  and  his  assistants 
wished  to  increase  progressively  the  virulence  of  the 
virus  of  chicken  cholera  and  splenic  fever,  so  as  to 
bring  them  at  last  to  their  maximum  intensity,  these 
viruses  were  first  inoculated  into  young  subjects,  and 
from  them  successively  into  oldejr  ones. 


THE  LABORATORY  OF  THE  ECOLE  NORMALE.     287 

'  The  Academy  remembers,  without  doubt,'  said 
Pasteur  in  a  recent  communication,  '  that,  some  time 
ago,  we  discovered  a  microbe  virus  in  the  saliva  of 
hydrophobia.  This  microbe,  though  very  virulent  for 
rabbits,  is  shown  to  be  harmless  for  adult  guinea-pigs, 
but  it  kills  rapidly  guinea-pigs  only  some  hours  or 
days  old.  In  following  out  this  inoculation  from 
young  guinea-pigs,  we  have  seen  the  virulence  increase, 
and  easily  arrive  at  the  point  of  causing  death  to 
older  guinea-pigs.  There  was  even  at  last  a  marked 
difference  in  the  lesions.  The  increase  of  virulence, 
by  successive  passages  through  individuals  of  one 
race,  was  clearly  shown. 

'  But  the  new  and  unexpected  result  that  I  wish  to 
point  out  to  the  Academy  consists  in  this :  that  ths 
microbe,  after  having  increased  its  virulence  by 
successive  passages  through  the  bodies  of  guinea-pigs, 
shows  itself  to  be  less  virulent  in  relation  to  rabbits 
than  it  was  before. 

'  In  these  new  conditions,  it  gives  to  the  rabbit  a 
disease  which  is  spontaneously  curable ;  and,  moreover, 
having  once  gone  through  the  malady,  the  animal  be- 
comes refractory  in  regard  to  the  microbe  which  is 
deadly  to  rabbits.  From  this  arises  the  all-important 
consequence,  that  the  habit  of  living  in  one  species 
(the  guinea-pig)  at  a  definite  corresponding  degree  of 
virulence,  can  change  this  virulence  in  relation  to 
another  species  (the  rabbit),  so  much  diminishing  its 


288  LOUIS  PASTEUR. 

effects  as  to  cause  -it  to  become  a  vaccine  for  this  latter 
species. 

'  The  importance  of  this  result  cannot  fail  to  be 
perceived  by  everyone,  for  it  contains  the  secret  of  a 
new  method  of  attenuation,  which  can  be  applied  to 
some  of  the  most  virulent  viruses.  We  will  give  an 
example  and  an  application  of  it. 

'  If  a  pigeon  be  inoculated  in  the  pectoral  muscle 
with  the  microbe  of  swine  fever,  the  pigeon  dies  in  an 
interval  of  six  or  eight  days,  after  having  shown  the 
apparent  exterior  symptoms  of  fowl  cholera. 

'  When  a  second  pigeon  is  inoculated  with  the  blood 
of  the  first,  a  third  with  that  of  the  second,  and  so  on 
in  succession,  the  microbe  acclimatises  itself  to  the 
pigeon.  The  symptoms  of  forming  itself  into  a  ball, 
and  of  somnolence,  which  are  the  habitual  character- 
istics of  the  disease,  appear  in  a  much  shorter  time 
than  with  the  first  pigeons  of  the  series.  Death 
likewise  comes  on  more  rapidly.  Finally,  the  blood 
of  the  last  pigeons  exhibits  much  more  virulence  in 
the  pig  than  even  the  most  infectious  products  of 
a  pig  that  has  died  of  what  is  called  spontaneous 
fever. 

'  The  passage  of  the  swine  fever  microbe  through 
rabbits  leads  to  quite  a  different  result.  Eabbits  ino- 
culated with  the  infectious  products  of  a  pig  that  has 
died  of  the  fever,  or  with  the  cultivations  of  them,  are 
always  made  ill  and  most  frequently  die. 


IRE  LABORATORY  OF  THE  ECOLE  NORMALE.  289 

*  When  the  virus  is  inoculated  from  rabbit  to 
rabbit,  the  microbe  acclimatises  itself  to  the  rabbit. 
All  the  animals  die,  and  death  comes  in  a  very  few  days. 
The  cultures  of*the  blood  of  these  rabbits  in  sterilised 
media  become  progressively  easy  and  more  abun- 
dant. The  microbe  itself  changes  its  aspect  somewhat, 
grows  rather  larger  than  in  the  pig,  and  appears  in 
the  form  of  an  8,  without  the  filiform  lengthening  out 
characteristic  of  certain  other  cultures. 

'  When  pigs  are  inoculated  with  the  blood  of  the 
last  rabbits,  and  the  results  compared  with  those 
obtained  from  the  first  of  the  series,  it  is  found 
that  the  virulence  has  been  progressively  diminishing 
from  the  first  rabbit  to  the  following  ones.  Very  soon 
the  blood  of  the  rabbits  ceases  to  cause  death  in  the 
pigs,  though  it  renders  them  ill.  On  recovery  they 
are  proof  against  the  deadly  swine  fever.' 


III. 

But  in  the  midst  of  these  investigations  undertaken 
by  Pasteur,  there  is  one  which  is  paramount  over  all 
the  others,  one  on  which  for  three  years  all  his 
efforts,  as  well  as  those  of  his  pupils,  have  been  con- 
centrated, and  this  is  Hydrophobia.  Mysterious  in  its 
incubation,  alarming  in  its  symptoms,  Pasteur's 
attention  had  for  a  long  time  been  drawn  to  it,  when 
in  1880  he  finally  attacked  it.  Besides  the  attraction 


290  LOUIS  PASTEUR. 

which  an  obscure  problem  had  for  him,  he  felt  that  if 
he  succeeded  in  discovering  the  probably  microbean 
etiology  of  such  a  disease,  he  would  carry  all  minds 
with  him  into  the  current  of  these  new  ideas.  He  had 
been  very  often  struck,  if  not  with  the  opposition,  at 
least  with  the  prudent  and  circumspect  reserve,  shown 
in  the  examination  of  his  doctrine,  by  a  considerable 
number  of  physicians  who,  possessed  by  the  idea  that 
the  moral  element  could  cause  modifications  in  the 
symptoms  and  development  of  a  malady  in  man,  are 
not  disposed  to  recognise  the  least  assimilation  between 
human  diseases  and  those  of  the  animal  species.  No 
doubt  the  emotional  qualities,  grave  family  cares,  the 
terror  of  approaching  death,  the  dread  of  the  great  un- 
known, may  modify  the  course  of  the  evil  in  man,  may 
aggravate  it,  even  hasten  it ;  but,  whilst  recognising — 
for  never  was  there  a  man  more  a  creature  of  senti- 
ment than  he — what  there  is  of  deep  truth  in  this 
opinion,  Pasteur  could  not  help  thinking  that  the  first 
origin,  the  cause  of  every  contagious  malady,  is  physio- 
logically the  same  in  the  two  groups,  and  that  our 
bodies,  notwithstanding  our  superior  moral  qualities, 
are  exposed  to  the  same  dangers,  to  the  same  disorders, 
as  the  bodies  of  animals. 

To  overcome  these  resistances,  it  was  necessary,  as 
in  the  great  experiments  on  splenic  fever,  to  attack  a 
disease  common  both  to  men  and  animals — one  in 
which  experimentation,  the  only,  but  great,  strength 


THE  LABORATORY  OF  THE  E~COLE  NORMALE.     291 

of  Pasteur,  was  supreme.  Hydrophobia  offered  these 
conditions. 

Again,  it  was  Dr.  Lannelongue  who  introduced 
Pasteur  to  his  first  case  of  hydrophobia.  On 
December  10,  1880,  a  child  of  five  years  old,  who 
had  been  bitten  in  the  face  a  month  previously,  was 
dying  in  the  Trousseau  Hospital.  Devoured  at  the 
time  by  a  raging  thirst,  and  seized  with  a  horror  for 
all  liquids,  he  approached  with  his  lips  the  spout  of  a 
closed  coffee  pot,  then  suddenly  started  back — the 
throat  contracted— a  prey  to  such  fury  that  he  insulted 
the  nursing  sister  who  was  attending  on  him.  He  was 
at  the  same  time  attacked  by  aerophobia  to  a  prodigious 
degree.  At  a  certain  moment,  the  heel  of  one  of  his 
feet  protruded  from  the  bed.  An  assistant  blew  on  it. 
The  child  had  not  seen  the  assistant,  and  the  breath 
of  air  was  so  light  as  to  be  almost  imperceptible.  The 
poor  child  flew  into  a  rage,  and  a  violent  spasm 
seized  him  in  the  throat.  The  next  day  delirium 
began,  a  frightful  delirium.  The  frothy  matters 
which  filled  his  throat  suffocated  him. 

Four  hours  after  his  death,  the  mucus  from  the 
palate  of  the  child  was  collected.  It  was  diluted  with 
a  little  water,  and  two  rabbits  were  inoculated  under 
the  skin  of  the  abdomen.  The  rabbits  perished  in 
less  than  thirty-six  hours.  The  saliva  of  these  dead 
rabbits  also  transmitted  the  disease  to  fresh  rabbits. 
Did  it  not  seem  as  if  one  had  got  hold  of  an  inocula- 


292  LOUIS  PASTEUR. 

tion  of  hydrophobia  ?  Such  was  in  fact  the  conclusion 
of  Dr.  Maurice  Kaynaud,  who,  having  been  informed, 
at  the  same  time  as  Pasteur,  of  the  illness  of  the  child, 
had  made,  on  his  own  account,  some  experiments  on 
rabbits.  His  rabbits  were  dead.  Already  a  year 
previously  M.  Maurice  Eaynaud  had  announced  the 
transmission,  by  the  saliva,  of  rabies  from  man  to 
rabbits.  '  We  are,  then,  in  the  presence  of  a  new  fact 
of  this  kind,'  he  said,  '  and  we  really  believe,  until  a 
proof  to  the  contrary  is  given  us,  that  these  latter 
rabbits  died  of  hydrophobia.' 

With  his  habitual  prudence,  and  trusting  more  to 
the  results  of  experiment  than  to  medical  observation 
alone,  Pasteur  was  not  in  a  hurry  to  form  such 
positive  conclusions.  He  began  by  doing  what  Dr. 
Maurice  Raynaud  had  neglected  to  do.  He  examined 
with  the  microscope  the  tissues  and  the  blood  of  the 
rabbits  inoculated  in  the  laboratory ;  he  discovered, 
both  in  those  that  were  dead,  and  in  those  which  were 
on  the  point  of  death,  the  presence  of  a  special 
microbe,  easily  cultivable  in  a  pure  state  and  of 
which  the  successive  cultures  caused  the  death  of 
other  rabbits.  Invariably,  the  same  microbe  appeared 
in  the  blood.  As  one  or  two  days  sufficed  to  cause 
death,  hydrophobia  could  not  have  had  time  to  make 
its  appearance.  Pasteur,  moreover,  found  this  same 
microbe  in  the  saliva  of  children  who  had  died  of 
common  maladies,  and  even  in  the  normal  saliva  of 


THE  LABORATORY  OF  THE  ECOLE  NORMALE.  293 

healthy  adults.  It  was  a  new  microbe,  causing  a 
disease  unknown  up  to  that  time.  To  Pasteur  it 
seemed,  in  the  case  of  the  experiments  made  with  the 
mucus  from  the  child's  palate,  to  be  simply  an  ac- 
companiment of  the  rabic  virus. 

This  microbe  of  the  saliva  is  very  easily  cultivated 
in  sterile  infusions — that  of  veal,  for  example — and 
successive  cultures  can  be  made  in  the  usual  way. 
The  virulence  continues.  Could  the  virulence  be  at- 
tenuated, asked  Pasteur,  by  the  action  of  the  oxygen  of 
the  air  ?  This  would,  by  a  new  example,  go  to  esta- 
blish the  generalisation  of  the  method  of  attenuation  by 
oxygen.  The  attempt  succeeded.  When  care  is  taken, 
as  with  the  attenuation  of  the  fowl  cholera  contagium, 
not  to  allow  more  than  seme  hours'  interval  to  elapse 
between  one  cultivation  and  the  succeeding  one,  the 
virulence  of  the  successive  cultivations  of  the  microbe 
of  the  saliva  is  preserved  in  some  sort  indefinitely.  In 
other  words,  if  it  be  arranged  that  the  cultures  succeed 
each  other  every  twelve  hours,  the  rabbits  inoculated 
from  the  last  cultures  die  as  quickly  as  those  inocu- 
lated from  the  first.  Thuillier  had  had  the  patience 
to  make,  in  this  manner,  eighty  cultures  in  contact 
with  air,  and  eighty  cultures  in  a  vacuum ;  the  mi- 
crobe of  the  saliva  being  both  aerobic  and  anaerobic. 
The  eightieth  culture  killed  as  quickly  as  the  first. 
But  by  allowing  the  successive  cultures  to  remain  for 


294  LOUIS  PASTEUR. 

some  time  in  contact  with  the  air,  before  passing  from 
one  culture  to  the  following  one,  the  virulence  of  the 
cultures  becomes  enfeebled.  Thus,  then,  as  in  fowl 
cholera,  attenuated  cultures  of  the  microbe  can  be  ob- 
tained. Unlike  what  happens  with  cholera,  however, 
the  cultures  of  the  microbe  of  the  saliva,  exposed 
to  the  contact  of  air,  perish  very  quickly.  Two  or 
three  days  of  keeping  suffice  for  the  parent  cultivation 
to  lose  all  virulence.  The  seed,  taken  in  any  quantity 
from  it,  does  not  fertilise  a  new  cultivation.  But, 
before  perishing,  this  culture  passes  through  very  differ- 
ent degress  of  progressively  weakened  virulence,  and 
it  is  easy  with  these  cultivations  to  render  rabbits  ill 
without  causing  their  death.  Once  cured,  they  resist 
all  inoculation  which  would  be  mortal  for  others. 
The  oxygen  of  the  air  is  manifestly  the  transformer  of 
this  virulent  virus  into  vaccine  virus ;  for,  if  the  viru- 
lent blood  or  cultivations  remain  inclosed  in  their 
tubes,  sealed  from  all  entrance  of  the  air,  they  retain 
not  only  for  some  hours,  but  for  months,  their  life  and 
their  original  virulence. 

But  though  these  results  were  as  new  as  they  were 
unexpected,  and  though  one  cause  of  confusion  in  the 
study  of  this  terrible  problem  was  removed,  yet  these 
first  researches  were  not  marked  by  any  progress  in 
the  etiology  of  hydrophobia.  The  question  remained 
wholly  unsolved. 


THE  LABORATORY  OF  THE  ECOLE  NORM  ALE.  295 

Impatient  with  the  length  of  time  required  for 
the  incubation  of  the  disease,  and  with  the  obligation 
of  waiting  whole  months  for  the  result  of  an  experi- 
ment, when  the  subject  demanded  such  numerous 
ones,  Pasteur  began  to  seek  some  means  of  producing 
hydrophobia  with  certainty  and  of  making  it  appear 
more  rapidly.  Notwithstanding  the  assertion  of  a 
professor  of  the  veterinary  school  at  Lyons  that  the 
saliva  of  the  rabid  dog  alone  contained  the  virus  of 
the  disease,  and  that  he  had  failed  in  every  attempt  to 
inoculate,  whether  with  the  substance  of  the  brain  or 
with  the  spinal  marrow  of  rabid  dogs ;  Pasteur,  with 
due  care  as  to  purity,  introduced  under  the  skin  of 
some  rabbits  and  some  dogs,  divers  parts  of  the  brain 
of  a  dog  which  had  died  in  a  rabid  state.  Hydro- 
phobia declared  itself  in  both  dogs  and  rabbits,  with  a 
duration  of  incubation  about  equal  to  that  which 
followed  the  ordinary  bite  of  a  dog.  Although  it  was 
necessary  still  to  submit  to  this  long  uncertainty  with 
regard  to  the  incubation,  one  great  result  was  obtained : 
hydrophobia  could  be  inoculated  with  other  matter 
than  saliva.  Not  only  is  the  saliva  always  impure, 
containing  a  saliva  microbe,  which  is  endowed  with 
a  special  virulence  of  its  own,  but  it  presents  other 
inconveniences.  It  is  necessary,  in  these  researches, 
to  have  a  supply  of  material  constantly  at  hand. 
Now,  the  saliva  loses  its  rabic  virulence  in  twenty- 
four  hours.  The  existence  of  the  rabic  virulence  in 
15 


296  LOUIS  PASTEUR. 

the  brain  substance  placed,  on  the  contrary,  at  the 
disposal  of  the  experimenter,  an  abundance  of  the 
virus,  in  a  state  of  great  purity  and  capable  of  long 
preservation. 

The  idea  then  occurred  to  Pasteur  and  his  assist- 
ants, to  inoculate  the  virulent  rabic  matter  in  its  pure 
state  under  the  dura  mater  on  the  surface  of  the  brain 
of  a  dog.  Why  not  carry  the  virus,  said  Pasteur, 
directly  to  the  place  of  its  activity  and  development  ? 
After  having  trepanned  the  skull  of  a  chloroformed 
dog,  a  little  bit  of  the  medulla  of  an  animal  which  had 
died  of  hydrophobia  was  deposited  on  the  surface  of 
the  brain.  As  soon  as  the  influence  of  the  chloroform 
was  dissipated,  the  dog  recovered  its  healthy  appear- 
ance. It  ate  its  food  that  same  evening.  But  after 
some  days  the  symptoms  of  hydrophobia  appeared. 
The  animal  became  dejected  and  restless ;  it  tossed 
its  litter  about,  refused  all  nourishment.  A  doleful, 
sharp  howling  was  the  first  indication  of  the  rabic 
voice,  which  is  but  one  long  cry  of  suffering  and 
appeal,  mingled  with  barkings  from  hallucinations. 
The  stomach  became  depraved ;  the  dog  swallowed  hay 
and  straw.  It  soon  grew  furious,  agitated  with  violent 
convulsions  ;  finally,  after  a  last  fit,  it  died.  During 
all  this  time  there  was  great  rejoicing  in  the  labora- 
tory. They  were  at  last  in  possession  of  a  method 
for  singularly  shortening  the  period  of  incubation,  and 


THE  LABORATORY  OF  THE  ECOLE   NORMALE.    297 

for  communicating  the  disease  with  certainty.  The 
experiments  were  multiplied ;  all  the  dogs  which  were 
trepanned,  and  which  received  on  the  surface  of  the 
brain  a  little  of  the  medulla  of  the  rabid  animal, 
succumbed  to  the  disease,  with  very  rare  exceptions, 
within  a  period  of  twenty  days.  Did  not  the  method 
pursued  demonstrate,  among  other  things,  that  hydro- 
phobia is  a  disease  of  the  brain ;  that  the  seat  of  the 
rabic  virus,  far  from  being  exclusively  in  the  saliva, 
belongs,  above  all,  to  the  cerebral  matter  ? 

Other  results,  in  addition  to  this  one,  were  not  slow 
in  revealing  themselves.  It  was  established  that  not 
only  the  brain,  but  the  spinal  marrow,  along  its  whole 
length,  may  be  rabic,  and  that  the  nerves  themselves 
throughout  their  whole  system,  from  the  centre  to  the 
periphery,  may  contain  the  virus  of  hydrophobia.  If 
there  exists  a  microbe  of  hydrophobia,  its  medium 
of  cultivation  in  the  body  is,  par  excellence,  the  brain, 
the  spinal  marrow,  and  the  nerves.  It  was  also 
established  that  there  were  localisations  of  virus  in 
certain  parts  of  the  mucous  system,  and  that  the  very 
considerable  differences  of  rabic  symptoms  which  exist 
in  different  cases  of  hydrophobia,  must  be  sought  for 
in  this  fact.  At  the  moment  of  death  the  medulla 
oblongata  is  always  rabic.  Finally,  it  was  established 
that  hydrophobia  could  be  given  (and  almost  as 
rapidly  as  by  trepanning)  by  inoculating  rabic  nervous 
matter  into  the  circulation  of  the  blood  by  a  vein. 


298  LOUIS  PASTEUR. 

In  presence  of  such  facts  it  is  easy  to  account  for 
what  takes  place  in  the  case  of  a  bite  from  a  mad  dog. 
The  circulation  of  the  blood  carries  the  virus  to  the 
surface  of  the  brain,  or  to  the  surface  of  the  spinal 
marrow;  there  it  houses  itself  in  particular  spots, 
and,  little  by  little,  invades  the  nervous  matter. 
This  last  would  be  progressively  attacked  throughout, 
if  death  from  the  medulla  oblongata  did  not  almost 
always  supervene  before  the  propagation  of  the  virus 
can  become  general. 

The  saliva  glands  are  often  rabic,  doubtless  because 
the  virus  oozes  into  them,  little  by  little,  from  the 
nerves  which  enter  these  glands.  Thus  may  the  pre- 
sence of  this  virus  be  explained  in  the  saliva  of  mad 
dogs,  where,  at  all  times  since  the  disease  was  first 
known,  it  has  been  found  to  exist.  When  the  first 
point  attacked  by  the  virus  is  the  spinal  marrow,  or 
certain  portions  of  it,  a  general  paralysis  often  pre- 
cedes death.  In  this  case  the  howling  and  biting 
symptoms  are  for  the  most  part  absent,  and  the  dog 
continues  to  be  caressing  until  it  dies. 

In  a  thesis  written  by  M.  Koux,  Pasteur's  labora- 
tory assistant,  last  July,  we  read  the  following : — '  If 
we  examine  with  care  a  little  of  the  pulp  taken  freshly 
from  the  brain  of  a  rabid  animal,  and  compare  it  with 
the  same  substance  from  the  brain  of  a  healthy 
animal,  it  is  difficult  to  distinguish  any  difference 
between  the  two.  In  the  rabic  pulp,  however,  besides 


THE  LABORATORY  OF  THE  ECOLE  NORMALE.     299 

the  granulations  which  are  found  in  profusion  in  the 
healthy  pulp,  there  seem  to  exist  little  grains  of  ex- 
treme minuteness,  almost  imperceptible  even  with  the 
strongest  microscopes.  In  the  cephalo-rachidic  liquid 
so  limpid  in  appearance,  it  is  possible  with  great 
attention  to  detect  similar  little  grains.  Can  this  be 
the  microbe  of  Irydrophobia  ?  Some  do  not  hesitate 
to  affirm  that  it  is.  For  ourselves,  as  long  as  the 
cultivation  of  the  microbe  outside  of  the  organism  has 
not  been  effected,  and  that  hydrophobia  has  not  been 
communicated  by  means  of  artificial  cultures,  we  shall 
abstain  from  expressing  a  definite  opinion  on  the 
subject.' 

But  the  grand  problem  in  regard  to  hydrophobia 
is,  not  so  much  the  isolation  of  the  microbe,  as  the 
finding  of  a  means  of  preventing  this  frightful  disease. 

Even  now  the  experiments  are  in  full  swing. 
Biting  dogs  and  bitten  dogs  fill  the  laboratory.  With- 
out reckoning  the  hundreds  of  mad  dogs  that  have 
died  in  the  laboratory  during  the  last  three  years, 
there  never  occurs  a  case  of  hydrophobia  in  Paris 
of  which  Pasteur  is  not  informed.  Not  long  ago 
a  veterinary  surgeon  telegraphed  to  him,  'Attack 
at  its  height  in  poodle-dog  and  bull-dog.  Come.' 
Pasteur  invited  me  to  accompany  him,  and  we  started, 
carrying  six  rabbits  with  us  in  a  basket.  The 
two  dogs  were  rabid  to  the  last  degree.  The  bull  dog 


300  -     LOUIS  PASTEUR. 

especially,  an  enormous  creature,  howled  and  foamed 
in  its  cage.  A  bar  of  iron  was  held  out  to  him  :  he 
threw  himself  upon  it,  and  there  was  great  difficulty 
in  drawing  it  away  from  his  bloody  fangs.  One  of  the 
rabbits  was  then  brought  near  to  the  cage,  and  its 
drooping  ear  was  allowed  to  pass  through  the  bars. 
But,  notwithstanding  this  provocation,  the  dog  flung 
himself  down  at  the  bottom  of  his  cage  and  refused  to 
bite. 

Two  youths  then  threw  a  cord  with  a  slip  loop 
over  the  dog,  as  a  lasso  is  thrown.  The  animal  was 
caught  and  drawn  to  the  edge  of  the  cage.  There 
they  managed  to  get  hold  of  him  and  to  secure  his 
jaws;  and  the  dog,  suffocating  with  fury,  his  eyes 
bloodshot,  and  his  body  convulsed  with  a  violent 
spasm,  was  extended  upon  a  table  and  held  motion- 
less, while  Pasteur,  leaning  over  his  foaming  head, 
at  the  distance  of  a  finger's  length,  sucked  up  into 
-a  narrow  tube  some  drops  of  the  saliva.  In  the  base- 
ment of  the  veterinary  surgeon's  house,  witnessing  this 
formidable  tete-a-tete,  I  thought  Pasteur  grander  than 
I  had  ever  thought  him  before. 


THE  STORY  OF  MY   LIFE. 

By  the  late  J.  MARION  SIMS,  M.  D.     Edited  by  his  Son,  H.  MAKION-SIMS, 
M.  D.     12mo,  cloth,  472  pages.     $1.50. 

"Marion  Sims,  by  himself  and  through  others,  has  restored  to  society  and 
to  happiness  an  ever-increasing  multitude  of  sufferers,  condemned,  before  he 
opened  the  way  of  escape,  to  life-loug  wretchedness.  For  himself  he  achieved 
such  renown  that  his  name  is  a  household  word  in  medical  circles  the  world 
over.  But  the  story  is  more  than  an  autobiography :  it  not  merely  illustrates  the 
evolution  of  a  South  Carolina  country  lad  into  one  of  the  most  usclul  and  con- 
spicuous of  modern  benefactors;  it  is  local  history  interpreting  rural  life  in 
that  section  fifty  years  ago."— New  York  Evening  Post. 

"  The  book  opens  with  a  very  interesting  introduction,  in  which  Judge  T.  J. 
Mackey  pays  a  deserved  tribute  to  the  distinguished  surgeon,  and  recapitulates 
the  achievements  upon  which  his  professional  fame  rests,  and  which  have  won 
him  recognition  in  Europe  and  America  as  the  foremost  clinical  surgeon  of  the 
nge.  Dr.  Sims  was  born  in  Lancaster  County,  S.  C.,  and  though  the  greater  part  of 
his  life  was  spent  away  from  his  native  State,  South  Carolinians  have  a  right  to 
feel  a  personal  pride  in  the  reputation  he  won." — Charleston  Ntvie  and  Courier. 

"  The  claim  of  Dr.  Sims  to  the  regard  of  posterity  rests  on  a  number  of  pro- 
fessional achievements  conferring  honor  on  both  himself  and  his  country.  Fii>t, 
he  invented  the  silver  suture  and  applied  it  successfully  to  cases  of  fistula,  until 
then  deemed  incurable.  Second,  he  invented  what  is  known  as  the  '  Sims  Sptc- 
nlum'— the  most  effective  now  known.  Third,  he  made  an  exposition  of  the 
pathology  and  true  method  of  trismus  natcentivm,  or  the  lock-jaw  of  infants. 
Fourth, "he  was  the  founder  and  organizer  of  the  Woman's  Hospital  of  the  State 
of  New  York,  the  first  institution  "ever  dedicated  exclusively  to  the  cure  of  the 
diseases  of  women.  Fifth,  he  made  valuable  contributions  to  medical  literature. 
The  story  of  a  life  so  full  of  usef  jlness  to  his  fellows  will  have  a  peimanent  value, 
and  will  be  widely  read  by  all  who  admire  the  benefactors  of  the  human  race." — 
Troy  Daily  Evening  Times. 

"The  medical  profession  will  find  a  peculiar  Interest  In  this  volume,  in  which 
the  great  physician  tells  the  story  of  his  career,  and  of  those  brilliant  discoveries 
and  inventions  which  have  given  renown  not  only  to  him,  bnt  to  the  entire  body 
of  American  medical  science.  In  his  special  departments  be  enlarged  the  scope 
of  surgery  for  the  whole  world,  and  it  is  not  too  much  to  sny  that  his  name  will 
stand  in  the  completed  history  of  the  science  as  one  of  its  illustrious  creators.  He 
was  not  less  distinguished  for  the  simple  virtues  and  noble  heroism  of  his  char- 
acter in  private  life,  than  for  his  successes  in  his  profession,  and  this  testament 
from  h'is  hand  will  commend  him  to  the  love  and  reverence  of  thousands  who 
have  only  known  him  hitherto  through  the  reports  of  fame." — N.  T.  Home  Journal. 

"The  late  Dr.  Sims  probably  obtained  a  wider  reputation  than  any  other 
American  physician.  His  brilliant  discovery  in  a  highly  important  but  obscure 
department  of  surgery  won  the  admiration  of  hie  profession  in  the  New  and  Old 
Worlds.  His  fame  culminated  in  this  country  as  far  back  as  1855,  when  the  Wom- 
an's Hospital  was  established  in  New  York  for  the  sole  purpose  of  curing  by 
his  method  a  trouble  that  had  previously  been  deemed  incurable.  The  leaders  in 
the  New  York  fashionable  society  of  that  day  took  charge  of  this  truly  philan- 
thropic work.  They  were  assisted  in  it  by  our  most  distinguished  local  physi- 
cians and  surgeons,  who  freely  testified  to  the  extraordinary  merit  of  Dr.  Sims's 
discovery.  For  nearly  thirty  years  this  institution  has  been  one  of  the  crowning 
mercies  of  New  York.  Dr.  Sims  in  this  work  tells  the  story  of  his  life  with  the 
utmost  fullness  and  frankness?.  Aside  from  his  claims  on  the  gratitude  of  woman- 
kind, the  doctor  had  a  history  well  worth  telling.  In  Paris,  London,  and  other 
capitals  of  Europe,  he  was  thrown  into  much  brilliant  society,  and  of  this  be  jots 
down  his  recollections  in  a  fresh  and  amusing  manner."— New  York  Journal  rf 
Commerce.  

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MAXIMS  OF   PUBLIC  HEALTH. 

By  0.  W.  WIGHT,  M.D.,  of  the  Detroit  Board  of  Health.     16mo,  cloth, 
75  cents. 

"  The  appearance  of  this  hand-book  is  most  timely.  There  is  a  vague  appre- 
hension that  the  cholera  may  visit  the  CTnited  States  next  year.  Everybody 
wants  to  know  what  to  do  for  the  exclusion  or  limitation  of  the  dread  disease. 
Dr.  O.  W.  Wight,  to  whom  we  owe  these  'Maxims  of  Public  Health.'  speaks 
with  the  voice  of  authority.  He  has  been  for  six  years  Health  Officer  of  Detroit, 
and  has  made  epidemics  the  subject  of  patient  aud  earnest  study.  Here  we  have 
the  fruits  of  all  bis  experience  and  observation.  His  book  ought  to  be  placed  in 
the  hands  of  every  person  connected  in  any  way  with  health  boards  in  all  parts 
of  the  country.  It  is  invaluable  for  instant  reference  in  an  emergency.  Dr. 
Wight  proves  his  competency  to  speak  on  this  subject  by  the  emphasis  lie  puts 
on  cleanliness  of  houses  and  streets  as  the  best  safeguard  against  pestilence." — 
New  York  Journal  of  Commerce. 

"Dr.  Wight  is  to  be  commended,  not  only  for  reiterating  the  dangers  to  which 
we  are  subject,  both  in  city  and  country,  from  unsanitary  surroundings,  but 
because  he  has  clothed  his  thoughts  in  virile,  understandable  English.  He  baa 
the  ordinary  scientific  view  of  filth  as  the  breeder  of  certain  contagious  diseases 
— scarlet  fever,  typhoid  fever,  diphtheria  and  the  like — but  has  a  new  idea  con- 
cerning the  removal  of  sewage  before  it  putrefies.  As  he  puts  it  in  the  preface, 
'  the  only  way  to  get  rid  of  sewer-gas  is  not  to  make  any.'  It  is  a  pleasure  to 
read  his  thoughts  ;  they  can  not  be  other  than  a  great  boon  to  the  unprofessional 
man,  for  whom  they  are  specially  written." — Hartford  Evening  1'ost. 

"The  intelligent  householder  who  has  no  time,  perhaps  no  inclination,  for 
systematic  studies,  may  read  these  maxims  with  a  quick  comprehension  of  their 
import,  and  find  hints  that  will  save  himself  and  his  loved  ones  unspeakable 
pain  and  sorrow.  To  say  nothing  of  his  success  as  a  medical  practitioner,  Dr. 
Wight  gives  in  this  valuable  book  the  result  of  six  years  of  personal  experience 
insanitary  administration.  We  heartily  commend  it  to  the  careful  reading  of 
all  who  would  be  prepared  to  ward  off  any  epidemic  that  should  make  its  appear- 
ance in  their  midst,  or  who  would  have  everything  about  their  premises  of  the 
most  healthful  character."— Boston  Home  Journal. 

"  Dr.  Wight's  heart  is  at  his  pen's  point  in  every  page  of  his  book,  and  he  is 
as  exhaustive  upon  every  phase  of  human  life  and  guttering  and  exposure  and 
economy,  as  he  is  on  the  school."— St.  Paul  Dispatch . 

"  A  little  volume  which  condenses  within  less  than  two  hundred  pages  a  vast 
amount  of  sanitary  science.  .  .  .  The  book  is  evidently  the  result  of  long  and 
close  attention  to  the  subject,  and,  being  designed  for  the  general  reader,  it  gives 
the  results  of  investigation  and  experiment  without  burdening  them  with  de- 
tails of  the  processes  by  which  they  have  been  reached.  It  is  a  book  which  should 
be  studied  by  all."—  Chicago  Daily  Times. 

"  This  is  a  timely  and  most  instructive  as  well  as  interesting  series  of  para- 
graphs on  sanitary  subjects,  which  ought  to  be  read  in  every  household  and 
hoard  of  health."— Newark  Daily  Advertiser. 

"He  plunges  into  the  subject  of  city  drainage,  handling  the  topic  with  such 
skill  and  precision  as  prove  him  a  past  master  of  hygienic  science.  Every 
possible  phase  of  house,  stable,  and  city  drainage,  and  sanitation,  is  explained 
and  discussed." — Detroit  Evening  News. 


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Vallery-Radot ,  Rene . 

Louis  Pasteur;  his  life  and  labours 


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